Autoecology of the marble trout - IdroLIFE...This river portion has a medium flow, alternating riffle and pools with a maximum depth of 1.8 m. The substrate is made up by sand (80%),

F C B D E A

Codice Azione

A.2.

Titolo Collection of abiotic, hydromorphological and biological

information necessary to plan concrete actions

Codice Subazione

Titolo

-

-

Tipo di elaborato Deliverable

Stato di avanzamento Final Version

Data 14.02.2020

Autori CNR – Istituto per lo Studio degli Ecosistemi

Responsabile dell’azione CNR – Istituto per lo Studio degli Ecosistemi

Collection of abiotic, hydromorphological and biological information

necessary to plan concrete actions

Autoecology of the marble trout Salmo

marmoratus in the Province of Verbano

Cusio Ossola

LIFE Nature and Biodiversityproject

LIFE15 NAT/IT/000823

Project title: Conservation and management of freshwater fauna of EU

interest within the ecological corridors of Verbano-Cusio-Ossola

Project acronym: IdroLIFE

Name of the Member State: IT - Italy

Start date: 15-11-2016

End date: 14-11-2020

Coordinating beneficiary CNR - Institute of Ecosystem Study (abbrev. CNR-ISE)

Associated beneficiaries Provincia del Verbano-Cusio-Ossola (PROVCO)

Ente Parco Nazionale della Val Grande (PNGV)

G.R.A.I.A. srl - Gestione e Ricerca Ambientale Ittica Acque (GRAIA)

Action A.2.

Action Title Collection of abiotic, hydromorphological and biological information

necessary to plan concrete actions

Subaction -

Subaction Title -

Title of the product Autoecology of the marble trout in the Province of Verbano Cusio Ossola.

Type of product Deliverable

Progress Final version

Date 14.02.2020

Authors CNR – Istituto per lo Studio degli Ecosistemi

Beneficiary responsible for

implementation CNR – Istituto per lo Studio degli Ecosistemi

Expected end date 15.06.2018

LIFE15 NAT/IT/000823 – “Action A.2. collection of abiotic,

hydromorphological and biological information necessary to plan concrete

actions ”

Pagina 3 di 28

3

Contents

1 INTRODUCTION ..................................................................................................................................... 4

2 STUDY SITES .......................................................................................................................................... 8

3 METHODS .............................................................................................................................................. 13

4 RESULTS AND DISCUSSION .............................................................................................................. 14

5 CONCLUSIONS ..................................................................................................................................... 22

6 REFERENCES ........................................................................................................................................ 24



actions ”

Pagina 4 di 28

4

1 INTRODUCTION

The present paper has the aim to describe the ecology of Marble trout (S. marmoratus) in the

Verbano-Cusio-Ossola province (VCO). In the following sections, after a brief species description,

a framing about the species ecology in VCO waters has been shown. This has been possible by

using all the 2017 data from IdroLIFE activities, integrating with previous data from surveys,

anglers catches and visual census.

Distribution

Marble trout, Salmo marmoratus (Cuvier, 1817), is an endemic salmonid, with of particular

conservation interest, that inhabits a very restricted geographical area belonging to the Adriatic

Basin from Po river (only northern tributaries) to Slovenian drainages of Soča and Rižana rivers

(Bianco 1987; Sommani 1961; Forneris et al. 1990; Schoffmann 1994; Povz 1995).

Morphological traits

First descriptions of the species (Gridelli, 1936; Pomini, 1937) highlighted the main differences

with the “stream trout”, the brown trout (Salmo trutta). Compared to this last one, marble trout has a

typical marbled pattern on its back and flanks and distinguishes itself for a big head (22-25% of the

Standard length) and for the absence of ocellated red spots and parr marks on its body (adult

specimens). It owns cycloid scales of small size, four teeth on the head of the vomer and vomer

stem is provided with 8 to 15 teeth, aligned but with the tips oriented right and left alternately. Fins

are well developed and caudal fin is homocercal, with back edge straight or slightly sunken

(Gandolfi et al. 1991; Delling et al. 2000; Kottelat and Freyhof, 2007).

Ecology

Besides the morphological aspects marble trout also differs from other ecological peculiarities; in

addition to the size (marble trout can reach 15-20 kg and exceed 1 meter length) this species prefers

the middle-low portion of cold water rivers (foothill area) overlapping its distribution with other

reofil species such as grayling (Thymallus sp.), insubrian barbel (Barbus caninus) and bullhead



actions ”

Pagina 5 di 28

5

(Cottus gobio). Exceptionally in december 2008 the first ever marble trout (95 cm length) from the

sea (Igrane-Croatia) has been recorded (Soldo, 2013). Furthermore, S. marmoratus (compared to

brown trout) seems to be more suited (over 60-70 cm length) to an ichthyophagous diet. In fact, in

the first years of life S. marmoratus feeds mainly of larvae and adults of aquatic and terrestrial

insects and with the increase in size, the diet is progressively oriented towards fish (conspecific

included).

Reproduction

Reproduction takes place from November to January, with water temperatures normally between 6

° and 8° C. Generally, the reproductive period lasts about a month, even if in some watercourses it

takes place only for a few days. Spawning is more intense in the early morning on new moon days.

Spawners run upstream in big rivers and their main tributaries to reach spawning sites. Males arrive

a few weeks before females. The deposition sites are located in shallow water (60 - 80 cm), with a

substrate characterized by pebbles and gravels and with a stream of about 0.4 - 0.5 m / s. The

female digs a shallow depression into the substrate and then lays her eggs. After fertilization by the

male, the mother covers the brood with nest’s gravel. Parental cares do not exist. Each female lays

an average of 1,700 - 2,800 eggs per kg of weight, with a diameter of about 5 - 6 mm and an orange

or yellowish color. Embryonic development requires a relatively long period depending on the

temperature of the water (about 40 days at 10 ° C). The fry remain buried in the gravel until the

yolk sac is reabsorbed. Male specimens reach sexual maturity towards the third year of age, females

at the same age or one year later (Zerunian, 2004).



actions ”

Pagina 6 di 28

6

Growth

Regarding S. marmoratus (Fig. 1) some of growth rates data available in literature are reported in

the following table (Tab. 1).

Tab. 1 – Age classes and corresponding lenght (mean ± S.D.) for Marble trout.

Author River 1+ 2+ 3+ 4+ 5+ 6+

Ielli, 1989 Avisio (Italy) 9-14 15-22 22-30 28-37 32-41 36-42

Vincenzi et al; 2007 Górska (Slovenia) 12.8 ± 2.0 19.2 ± 3.6 23.8 ± 3.9 27.5. ± 4.1 32.3 ± 2.2 36.0 ± 00

Vincenzi et al; 2007 Zakojska

(Slovenia) 11.5 ± 1.5 17.6 ± 2.7 21.1 ± 2.9 24.2 ± 3.1 28.0 ± 3.5 32.9 ± 2.4

Vincenzi et al; 2007 Gatsnik (Slovenia) 10.7 ± 1.5 16.3 ± 2.2 21.4 ± 2.6 27.0 ± 2.5 - -

Sumer et al; 2001 Trebusčica (Slovenia) 13.3 ± 1.0 17.4 ± 1.4 21.8 ± 1.0 28 ± 0.5 - -

Status

Species’ status at present time is considered critical due to introgression by brown trout strains.

Hybrids between the two forms are fertile and actually more abundant in many rivers of the species’

range (Meldgaard et al., 2007). This genetic affinity with S. trutta, moreover, underlines the species

'fragility' and the realistic risk of a complete genetic introgression leading to its disappearance.

Lastly, also the human impact represents a heavy factor responsible for the species decline: water

withdrawals, reduction of minimum vital flows, overfishing, pollution and alien species

introduction (brown trout over all) have contributed to list marble trout in the Annex II of the

European Union Habitats Directive 92/43/EEC and in the Red List (IUCN, 1996).



actions ”

Pagina 7 di 28

7

Fig. 1 - Marble trout (Salmo marmoratus), Toce river.



actions ”

Pagina 8 di 28

8

2 STUDY SITES

In this section Tab. 2 shows sites name and numbers with corresponding altitude, while the map

(Fig. 2) shows their geographical position. The figure includes data from the past (Regione

Piemonte, 1991 and G.R.A.I.A. s.r.l. samplings, 1995-1999) about Salmo marmoratus distribution

in Verbano-Cusio-Ossola (VCO) Province.

Fig. 2 - Numbers from 1 to 13 represent IdroLIFE sites; circular spots (red and white) represent past data about

marble trout distribution in the VCO Province.



actions ”

Pagina 9 di 28

9

Tab. 2 - IdroLIFE sites. (U)=upstream, (D)=downstream.

Toce River site (IdroLIFE activities) Site number m.a.s.l.

Gravellona Toce 1 211

Migiandone bridge (D) 2 215

Pieve Vergonte 3 232

Vogogna 4 226

Prata Dam (D) 5 227

Prata Dam (U) 6 229

Six Arches bridge (D) 7 239

Six Arches bridge (U) 8 240

Mizzoccola bridge (D) 9 261

Mizzoccola bridge (U) 10 263

Lake Tana (D) 11 302

Lake Tana (U) 12 304

Crodo 13 412

Sites description

1) Gravellona Toce

It is the last section of Toce river, close to the mouth. The riverbed reaches considerable amplitudes

(more than 60/70 m). Water depth is between 1 m and 5 m and banks are made up of large boulders.

This site is characterized by a low heterogeneity of habitats and a smooth flow.

2) Migiandone bridge (D)

It is the first main obstacle that fish find on their migrations. Under the bridge there’s a jump of 2 m

and only with high water levels it is possible to overcome this barrier (mostly for big fish). The

sampling, due to the persistent high water level, has been conducted 300 m downstream in a lateral

portion of the river, with a smooth flow and characterized by a substrate made by sand, gravel and

boulders. (Max depth 1m).



actions ”

Pagina 10 di 28

10

3) Pieve Vergonte

This river portion has a medium flow, alternating riffle and pools with a maximum depth of 1.8 m.

The substrate is made up by sand (80%), gravel (10%) and rocks (10%). On the hydrographic right

there is an artificial bank characterized by big boulders (Fig. 3C).

4) Vogogna

This sampling site is nearby the mouth of the Anza stream and it is characterized by a riverbed with

an amplitude of 30 m and maximum depth of 1.5 m. The substrate is made by sand and rocks while

the hydrographic left consists of a big bank made by artificial boulders. In this site water

temperature and transparency are influenced by Anza’s flow.

5) Prata Dam (D)

This site is located before the dam in an area where fishing is forbidden. The substrate is various,

with sand, gravel and big boulders. The depth can reach 3 m in the middle of the pool. The high

heterogeneity of this site allows the fish to find different types of refuge (Fig. 3A).

6) Prata Dam (U)

This site is located 300 m upstream the dam. The riverbed has an amplitude of 50 m, a smooth flow

and a substrate composed of sand and sporadic macrophytes. The maximum depth reaches 2 m (Fig.

3B).

7) Six Arches bridge (D)

This site is made by several pools downstream the natural barrier created by big boulders. The

substrate is made by rocks, gravel, sand and some boulder. The flow is various and alternates fast

flowing water with smooth flows and pools (Fig. 3D).

8) Six Arches bridge (U)

This spot has the main riverbed on the hydrographic right while on the left it owns a narrow

secondary arm with a complex system of vegetation on its banks and consequently with a high



actions ”

Pagina 11 di 28

11

percentage of shading. The main arm has a medium flowing water and a substrate made by sand,

gravel, rocks and some sporadic boulder.

9) Mizzoccola bridge (D)

This site is placed near the town of Domodossola, in the middle section of the river. A cochlea for

electricity production (and its fish passage) influences the riverbed hydrology on the left arm, while

on the right arm, several boulders placed alternately constitute a “natural” fish passage. The

substrate is made by gravel and rocks and the flow is medium-fast. Still on the left side of the bed

(in the left arm) there is a sectioned bank made by big boulders that during the sampling activities

have proven themselves as good shelters (Fig. 3E).

10) Mizzocola bridge (U)

This river area is made by a long flat section with a smooth flow and low depth (60-70 cm max.)

The substrate consists of gravel and rocks with some sporadic boulder. At the end of the sampling

site (hydrographic right) there is a deep pool (1.8 m) with some submerged boulders. This deep

refuge is due to the presence of an oil pipeline pylon.

11) Lake Tana (D)

Site 11 is placed exactly downstream the dam that creates the Lake tana. This is most probably the

last potential river area that a fish may potentially reach in its migration from downstream (or from

Lake Maggiore). The riverbed is highly artificial with banks made of concrete as well as the

substrate. Sand is present due to the lake deposit which moves downstream when dam’s gates are

completely open. The maximum depth reaches 1.7 m in the middle of the pool.

12) Lake Tana (U)

This site starts upstream the Lake tana, where the river has a smooth flow with the presence of a

couple of pool (maximum depth of 1.7 m). The substrate presents all the granulometry types, from

sand to some rare boulder. At the end of the site, hydrographic right, Toce meets the water of an

artificial canal, which on summer season brings cold and oxygenated waters exactly before the Lake

tana entrance (Fig. 3F).



actions ”

Pagina 12 di 28

12

13) Crodo

It is the site at the highest altitude. The riverbed is narrow and the hydrology is more typical of a

fast flowing alpine stream, where riffle zones are followed by smooth flows. The substrate

alternates gravel, rocks and boulders. The maximum depth reaches 70 cm maximum.

Fig. 3 - Six IdroLIFE sites: A) Prata dam downstream, B) Prata dam upstream, C) Pieve Vergonte, D) Six Arches

bridge downstream, E) Mizzoccola bridge downstream, F) Lake Tana upstream.

D

5

E F

C

A B



actions ”

Pagina 13 di 28

13

3 METHODS

Sampling activities have been conducted following the downstream-upstream gradient each

transect. The electrofishing device was a built-in-frame ELT60 IIGI (Scubla Acquaculture, 1,300

W, 600 V, DC current) set up with a copper cathode (width 2.5 cm, length 300 cm) and with a steel

ring anode (thickness 0.8 cm, diameter 40 cm). The fish collected were all individually measured

(total length, LT), weighed (total body mass, WT) and scales were taken for age determination by a

special magnifier (33x).

The body mass-length relationship was calculated using the equation:

W = a x Lb

The "b" coefficient usually is included between 2.6 and 3.4, representing a synthetic indicator of the

corpulence of the population’s individuals, and indirectly indicates their health state (Froese, 2006).

Length-at-age data were used to estimate the parameters of the Von Bertalanffy (1938) growth

function (VBGF) according to the equation:

LT= Linf (1-e-K(t-t0)

)

where LT is total length of the fish at time t, Linf is the theoretical maximum length an average fish

could achieve, k is the growth constant which determines how fast the fish approaches L∞, and t0 is

the hypothetical age at LT = 0.

Lastly, Linf, length at first maturity Lm (the length where the 50% of the fish in a population reach

sexual maturity) and optimal capture length Lopt (the intermediate length class where the product of

individuals times their average weight, reaches a maximum) have been obtained also through an

empirical equation from a specific excel spreadsheet created by Froese & Binohlan (2000).

As a management tool the PSD (Proportional Stock Density Index) index has been used (Volta,

2010). PSD is calculated as:

PSD= (Ni≥ Lm)/(Ni≥Lstock)*100

Ni = number of individuals

Lm = minimum quality length = mean length at maturity.

Lstock = minimum stock length = Lm-(LTrophy-Lm)/3



actions ”

Pagina 14 di 28

14

Ltrophy = Ltot ≥ 0.8*(Linf)

Linf is the site-specific maximum length reached by the species in that environment.

In order to obtain a more detailed picture on the species ecology in Toce river (in particular about

growth dynamics and on the related parameters), additional information from grey literature,

recreational and professional fishing have been considered and used in the excel spreadsheet.

4 RESULTS AND DISCUSSION

In the following table (Tab. 3), all data from IdroLIFE sampling activities have been resumed. Sites

progression from 1 to 13 follows the altitudinal gradient (1 lowest site, 13 the highest).

Tab. 3 - Results of sampling campaigns. Sites number (code), number of fish caught, morphometric

characteristics, measured lengths and weights have been shown. Additionally, brown trout presence is indicated

in each sampling site.

Site N° marble t. Min

lenght

Max

lenght

Mean

±S.E.

Min

Weight

Max

Weight

Mean

±S.E.

Min Age

years

Max Age

years

Brown t.

presence

1 0 - - - - - - - - X

2 22 7.3 8 7.6 ± 0.3 3.9 5.1 4.5 ± 0.6 0+ 0+ X

3 22 13.7 15.9 14.8 ± 1.1 27.4 41.2 34.3 ± 6.8 1+ 1+ X

4 21 15 65 23.7 ± 2.3 33.1 2554.3 234.6 ± 117.7 1+ 8+ X

5 21 28.5 65 44.4 ± 2.1 230.0 2650.0 1067.2 ± 168.1 3+ 6+ X

6 0 - - - - - - - - X

7 25 6.3 55 24.4 ± 4.1 2.0 1100 282.4 ± 99.4 0+ 5+ X

8 15 15 27 20.2 ± 1.9 33.2 189.2 89.4 ± 26.7 1+ 3+ X

9 28 8.5 32 21.2 ± 2.8 7.0 367.0 156.6 ± 54.4 0+ 3+ X

10 26 10 18 14.2 ± 1.4 9.9 61 34.0 ± 8.9 0+ 1+ X

11 0 - - - - - - - - X

12 16 24.8 68 40.2 ± 2.2 158.0 2580 723.6 ± 139.8 3+ 9+ X

13 7 20 38.5 26.8 ± 2.6 74.0 367.0 195.0 ± 42.9 2+ 3+ X



actions ”

Pagina 15 di 28

15

On 13 sites totally sampled, marble trout (203 specimens in total) has been recorded in 10 sites

whilst in 3 sites (1-Gravellona, 6-Prata dam upstream and 11-Lake Tana downstream) was absent.

On the contrary, the brown trout was sampled in every site, although in a limited number.

The highest maximum length has been recorded in site 12 (Lake Tana upstream), while the fish

with the maximum weight has been found in site number 5 (Prata dam). The maximum age

recorded (9 years) is from site 12 (Lake Tana upstream) while the “young of the year” class appears

in four sites on ten in which S. marmoratus showed its presence.

In the next lines, length-age relationship for marble trout has been reported (Fig. 4)

Fig. 4 - Age-length relationship for S. marmoratus (Toce river).

Length-weight relationship follows in the next figure (Fig. 5). Looking at the b parameter of the

relationship, S. marmoratus from Toce river has a value that falls within the widest range of values

(from 2 to 4) considered acceptable (Carlander, 1969). Furthermore, b parameter (3.0118) is slightly

higher than 3, indicating substantially an allometric growth.



actions ”

Pagina 16 di 28

16

Fig. 5 - Length-weight relationship for S. marmoratus (Toce river).

Focusing on the analysis on life-traits parameters, three different scenarios (A, B & C) are

generated in regard to the body growth of the fish (Tab. 5):

SCENARIO A: deriving the parameters shown in Table 5 by using the Von Bertalanffy

equation, the highest Linf among all is obtained. If subsequently this Linf value is entered in

the excel spreadsheet (Froese & Binholan, 2000), it is possible to obtain Lm and Lopt, and

even in this case both values are the highest of all 3 scenarios.

SCENARIO B: processing all IdroLIFE data through Froese & Binholan (2000), starting

from the maximum length of marble trouts caught by electric fishing in Toce river

population (68 cm), the lowest values for all the parameters (Linf, Lm and Lopt) are

obtained,

SCENARIO C: this last scenario has been originated by using data from anglers. After a

brief but detailed research it has been possible to get some information about the maximum

lengths recorded for S. marmoratus in the Toce river in these last 3 years. There are few

records of fish around and over 1 meter of length and several over 90 cm (Fig. 9). The

reasonable Lmax used for this scenario is at least 100 cm. The values for parameters Linf,

Lm and Lopt are placed halfway between the values from scenarios A and B.



actions ”

Pagina 17 di 28

17

Tab. 5 - Lmax, Linf, Lm and Lopt for Marble trout in Toce river (95% ± C.I.).*Calculated by using the

empirical equation from (Froese & Binholan, 2000).

Source Lmax (cm) Linf (cm) Lm (cm) Lopt (cm)

A) Von Bertalanffy, 1938 68.0 164.7 ± 17.5 81.8 ± 20.4* 100.3 ± 20.7*

B) Froese & Binholan, 2000 68.0 70.4 ± 1.7* 38.1 ± 6.1* 42.9 ± 8.0*

C) Extra info (anglers, grey

literature)

100.0 102.8 ± 3.1* 53.6 ± 10.4* 62.7 ± 12.1*

Robustness and accuracy of the Von Bertalanffy equation (and consequently of the curve and the

parameters derived from it) increase with the increase in the number of data for each individual age-

class. The reason why parameters derived through Table 5 are higher (Scenario A) compared to

others (B and C) depends on the reduced data pool. In particular, small abundances of individuals

belonging to age-class 4+ and to the following ones are reflected in the curve’s coefficient, which

generates likely an overestimation of the Linf parameter and consequently of Lm and Lopt when

computed with the excel spreadsheet.

Lowest parameters calculated in the B scenario by using data achieved from field samplings and

Froese and Binholan (2000) spreadsheet (starting from the maximum length sampled), may depend

instead on a sampling bias. In fact, a sampling carried out without the use of a boat don’t allow to

reach the deepest pools, where often larger marble trouts hide themselves. Because of this possible

bias, an underestimation of the maximum length (Lmax) recorded from data pool is obtained and,

consequently, low values for the remaining parameters derived from the excel spreadsheet equation.

By using data from anglers (scenario C), it has been possible to enrich the data set of river Toce

population even with large-sized specimens. Based on this addition, the parameters obtained are

more reliable and fit better to the ecology of a large foothill river fish, a river that in this case is

interconnected with a lake. In fact, Lake Maggiore is an important suitable habitat for marble trout

as pointed out by Gibertoni et al., (2017) the existence of a migratory lacustrine marble trout (Fig.

8) that during its life migrates (mainly for spawning) from Lake Maggiore to Toce river and

viceversa, has been documented. This lacustrine form seems to have a particular morphology

(larger dimensions, silvering colour and caudal fin with a “swallow tail” shape) compared to the

riverine marble trout (Fig. 9). Overall its growth rate seems to be significantly higher compared to



actions ”

Pagina 18 di 28

18

resident specimens (Tab. 6). The rapid growth rate of lacustrine trout ecotypes has also been found

in other environments (Merlo,1956; Gratton et al., 2004, Turin et al., 2006).

Tab. 6 - Lmax, Linf, Lm and Lopt for Marble trout in Toce river (95% ± C.I.).*Calculated by using the empirical

equation from (Froese & Binholan, 2000).

Source Species Water body Class 3+ Class 4+

This paper Marble trout Toce river 29.5 ± 4.4 cm 40.0 ± 5.7 cm

Gibertoni et al.,

2017

Migratory lacustrine

marble trout

Lake Maggiore,

Toce River

49.6 ± 2.7 cm 62.8 ± 4.9 cm

Merlo, 1956 “Lake trout” Lake Garda 37.8 ± 1.0 cm 41.6 ± 1.0 cm

Fig. 8 -Migratory lacustrine marble trout. Toce river (2017).



actions ”

Pagina 19 di 28

19

Fig. 9 – Two very large specimens from Toce river basin caught by amateur anglers (year 2017).

Regarding the growth rate of marble trout, Toce river fish (Tab. 4) have higher average length at

age than other rivers for which growth data are available (see Tab. 1). Furthermore, the structure of

the population shows more age classes, including fish with an age up to 9+, while the maximum

reported from other rivers is 6+ (Fig. 7).

Tab. 4 - Marble trout (Toce river) age classes and corresponding total lenght (mean ± S.D.).

0+ 1+ 2+ 3+ 4+ 5+ 6+ 7+ 8+ 9+



actions ”

Pagina 20 di 28

20

Toce river 8.0 ± 1.5 16.0 ± 2.0 21.2 ± 3.7 29.5 ± 4.4 40.0 ± 5.7 43.4 ± 3.7 53.7 ± 3.8 57.0 65.0 68.0

Fig. 7 - Comparison between Toce river lengths (mean values) separated by age-classes and other rivers values

available from literature.



actions ”

Pagina 21 di 28

21

Fig. 8 – Marble trout (young of the year).

After this previous multiple scenarios analysis the PSD index has been calculated starting from the

C scenario’s parameters. The PSD obtained starting from a Linf of 102.8 cm is 50. As a very

general approach, a population of fish is considered “in balance” if the PSD value is between 30 and

70 (Guy et al., 2007). In fact, if the PSD value is very low then there are few large fish in the

population, whereas a very large PSD indicates that there are few small fish in the population. In

this specific case of study the PSD shows reference conditions, beeing exactly in the middle of the

optimal range and it indicates that marble trout from Toce river has a balanced population.



actions ”

Pagina 22 di 28

22

Fig. 6 - Marble trout Length-frequency distribution (Toce river)

5 CONCLUSIONS

The purpose of this deliverable was to provide a picture of the autoecology of the marble trout in

the VCO province, and specifically in the Toce River, one of the last rivers in Italy inhabited by this

endemic salmonid. Thanks to the sampling activities related to action A.2 of the IdroLIFE project, it

has been possible to collect a dataset that helped to analyse the main biological characteristics of

this species and hypothesize strategies to its conservation on the long term.

In the following lines some suggestion on the management of the species are indicated.

the minimum capture lengths established in the VCO province for marble trout and for the

“lake trout” in general are respectively 35 cm and 40 cm (Provincia VCO, 2018). These

lengths are totally inadequate if compared with what emerges from this study. In fact,

looking at the scenario B (a scenario that underestimates all the parameters deriving from

the maximum recorded length) a Lopt of more than 40 cm is still obtained and by



actions ”

Pagina 23 di 28

23

completing the dataset with information derived from recreational anglers, the optimal

length of capture increases further by over 60 cm.

Concerning population dynamics, the presence of a structured population highlighted in this

study may depend to a relevant contribution of local hatcheries, annually introducing several

hundred thousand of fry along the river. At present we did not go deeply in genetic analyses

of the fish captured in the river and those from the anglers hatcheries, so it is not clear how

much the restocking from the hatcheries has a role in maintaining a balanced population in

the river.

The brown trout (Salmo trutta, atlantic strain - Fig. 10) is still present in all the sampling

site, although not very abundant. As already pointed out by Gibertoni et al. (2017) up tp

45% of the genetic structure of phenotypically identified marble trout in Toce River

indicates the presence of alleles of atlantic origin. In this regard, the brown trout is still a

threat to the existence of a pure marble trout population.

Fig. 10 - Salmo trutta

Management of Marble trout in the Toce river Basin: suggestions to improve its

conservation status

On the base of our results, we do think that different approaches must be taken in order to

improve the conservation status of marble trout in toce River Basin:

1. The first step to protect S. marmoratus is to increase the minimum length of capture

close to the optimum length. Increasing the minimum capture length (based on the Lopt

obtained from these data) allows the species to reach sexual maturity with a greater



actions ”

Pagina 24 di 28

24

percentage of individuals compared to percentage reached with the current minimum

capture length, thus helping to increasing the spawning stock and the resilience of the

population in regard to all stressors. Moreover, investing more to protect natural

reproduction is always preferable to the result achieved from artificial reproduction. In

fact, the fish grown in the hatchery may have a negative correlation with parameters

such as genetic variability, survival rate, growth rate, antipredator behaviour and fitness

in general (Reisenbichler and McIntyre, 1977; Kostow 2004; Jackson and Brown 2011;

Araki et al., 2008).

2. Prohibit further brown trout introductions in the lower stretch of the Toce River and in

Lake Maggiore. Avoiding the introduction of brown trout in Lake Maggiore, in the main

course of the river Toce and in the last stretches of the main tributaries would allow the

marble trout to re-establish an ever less introgressed population through the years. It

must be noted that the marble trout, due to its faster growth than brown trout, could

outcompete the latter when it is not massively stocked (Sommani 1961).

3. Increase the quality and genetic diversity of fish used for repopulation by a preliminary

selection of pure marble trout.

Alessio G., Bellardi S., Cauvin E., Forneris G., Giannatelli R., Palmegiano G.B., Quaglino G.,

Sacchi P., (1990). Caratterizzazione e biologia riproduttiva di una popolazione di Salmo Trutta

Marmoratus Cuv. del torrente Pellice (provincia di Torino). Rivista di Idrobiologia 29: 35-49.

Araki H., Berejikian B.A., Ford M.J., Blouin M.S., (2008). Fitness of hatchery‐ reared salmonids in

the wild.Evolutionary Applications, 1:342–355.

Bianco P.G., (1987): L'inquadramento zoogeografico dei pesci d'acqua dolce d'Italia e problemi

determinati dalle falsificazioni faunistiche. Atti II Conv. AIIAD, Torino, 41-66.

Carlander K.D., (1969). Handbook of freshwater fishery biology, volume 1. The Iowa State

University Press, Ames. Iowa. 752 p.



actions ”

Pagina 25 di 28

25

Crivelli A.J., (1995). Are fish introductions a threat to endemic freshwater fishes in the Northern

Mediterranean region? Biological Conservation 72: 311-319.

Cuvier G., (1817). Le Regne Animal, distribue d'apres son organisation, pour servir de base a

l'histoire naturelle des animaux et d'introduction a l'anatomie comparee. Deterville, Paris. 653 pp.

Delling B., Crivelli A. J., Rubin J-F., Berrebi P., (2000). Morphological variation in hybrids

between Salmo marmoratus and alien Salmo species in the Volarja stream, Soca River basin,

Slovenia. Journal of Fish Biology 57, 1199–1212.

Forneris G., Del Mastro G.B. & Bellardi S., (1990). Attuale distribuzione di Salmo marmoratus

Cuvier, 1817 in Provincia di Torino. Rivista di Idrobiologia 29: 213–221.

Froese R., (2006). Cube law, condition factor and weight–length relationships: history, meta-

analysis and recommendations. J. Appl. Ichthyol. 22, 241–253.

Froese R. & Binohlan C., (2000). Empirical relationships to estimate asymptotic length, length at

first maturity and length at maximum yield per recruit in fishes, with a simple method to evaluate

length frequency data. J. Fish Biol. 56, 758–773.

Gandolfi G., Zerunian S., Torricelli P., Marconato., (1991): I pesci delle acque interne italiane. Ist.

Poligrafico e Zecca dello Stato, Roma.

Gibertoni P., Penserini M., Esposito S., Foglia A., Dagani D., Bazzoni P., Rubin J-F., Fumagalli L.,

(2017). Osservazioni e studi preliminari su di una popolazione di trota marmorata (Salmo trutta

marmoratus) migratrice del fiume Toce e del lago Maggiore. Italian journal of freshwater

ichthyology, Vol 1.



actions ”

Pagina 26 di 28

26

Gratton P., Allegrucci G., Sbordoni V., Gandolfi A., (2004). The evolutionary jigsaw puzzle of the

surviving trout (Salmo trutta L. complex) diversity in the Italian region. A multilocus Bayesian

approach Author links open overlay panel. Molecular Phylogenetics and Evolution, 79:292-304.

Gridelli E., (1936): I pesci d'acqua dolce della Venezia-Giulia. Udine.

Guy, C., R. M. Neumann, D. W. Willis, Anderson R., (2007). Proportional size distribution (PSD):

A further refinement of population size structure index terminology. Fisheries, 32:348.

Kostow K.E., (2004). Differences in juvenile phenotypes and survival between hatchery stocks and

a natural population provide evidence for modified selection due to captive breeding. Canadian

Journal of Fisheries and Aquatic Sciences, 61(4): 577-589.

Kottelat M., Freyhof J., (2007) ‐ Handbook of European Freshwater Fishes. Kottelat, Cornol,

Switzerland and Freyhof, Berlin, Germany. 646 pp.

Ielli F., (1989) ‐ Accrescimento, alimentazione e riproduzione di una popolazione di trota

marmorata, S. trutta marmoratus Cuv., in Trentino Alto Adige. Tesi di Laurea in Scienze

biologiche, Facoltà di Scienze matematiche, fisiche e naturali, Università di Parma, 98 pp.

IUCN., (1996). 1996 IUCN Red List of Threatened Animals. IUCN, Gland, Switzerland.

Jackson C.D., Brown G.E., (2011). Differences in antipredator behaviour between wild and

hatchery-reared juvenile Atlantic salmon (Salmo salar) under seminatural conditions. Canadian

Journal of Fisheries and Aquatic Sciences, 68(12): 2157-2166.

Marconato A., Salviati S., Maio G, Marconato., (1986): La distribuzione dell'ittiofauna nella

provincia di Vicenza. Ed. Amministrazione Provinciale di Vicenza, Vicenza.

https://en.wikipedia.org/wiki/Molecular_Phylogenetics_and_Evolution



actions ”

Pagina 27 di 28

27

Meldgaard T., Crivelli AJ., Jesensek D., Poizat G., Rubin J-F., Berrebi P., (2007) Hybridization

mechanisms between the endangered marble trout (Salmo marmoratus) and the brown trout (Salmo

trutta) as revealed by in-stream experiments. Biological conservation 136: 602-611.

Merlo S., (1956) Accrescimento e ciclo vitale della trota lacustre (Salmolacustris L.) del Garda.

Italian Journal of Zoology, 23:2, 349-357.

Pomini F.P., (1937): Osservazioni sull'ittiofauna delle acque dolci del Veneto e indagini riguardanti

la Pesca. Boll. Pesca Piscic. Idrobiol., 13:262-312.

Povz M., (1995). Status of freshwater fishes in the Adriatic catchment of Slovenia. Biological

Conservation 72: 171–177.

Regione Piemonte., (1991). Carta ittica relativa la territorio della Regione piemontese. Assessorato

caccia e pesca. Torino (II Vol).

Reisenbichler R., McIntyre J.D., (1977). Genetic Differences in Growth and Survival of Juvenile

Hatchery and Wild Steelhead Trout, Salmo gairdneri. Journal of the Fisheries Research Board of

Canada, 34(1): 123-128

Schoffmann J., (1994). Zur gegenwa¨tigen Situation des marmorierten Forelle (Salmo marmoratus

Cuvier, 1817) in Albanien, ihrem su¨dlichsten Verbreitungsraum. Osterreichs Fischerei 47: 132–

136.

Soldo A., (2013): First marine record of marble trout Salmo marmoratus. Journal of Fish Biology 82,

700–702.

Sommani E., (1961). Il Salmo marmoratus Cuv.: sua origine e distribuzione nell’Italia

settentrionale. Bollettino di Pesca, Piscicoltura e Idrobiologia 15: 40–47.

https://eurekamag.com/research/036/743/036743540.php



actions ”

Pagina 28 di 28

28

Splendiani A. , Fioravanti T. , Giovannotti M. , Olivieri L. , Ruggeri P. , Nisi Cerioni P. , Vanni S. ,

Enrichetti F., Caputo Barucchi V., (2017). Museum samples could help to reconstruct the original

distribution of Salmo trutta complex in Italy. Journal of Fish Biology 90: 2443-2451.

Sumer S., Leiner S., Povz M., (2001). Marble trout (Salmo marmoratus) and bullhead (Cottus

gobio) in two Slovene rivers (Adriatic sea basin). Annales 11, 29-34.

Turin P., Zanetti M., Bilò M. F., (2006). Distribuzione e stato delle popolazioni di trota marmorata

nelle acque del bacino dell’Alto Adriatico. Biologia Ambientale 20 (1): 39-44.

Vincenzi S, Crivellı` AJ, Jesensek D, Rubin J-F, De Leo GA., (2007). Early survival of marble trout

Salmo marmoratus: evidence for density dependence? Ecology of Freshwater Fish: 16: 116–123.

Volta, P., (2010). Analysis of the population structure of Coregonus lavaretus (Linneus 1758) in

three deep Italian lakes using stock density indexes. Studi Trentini Scienze Naturali 87, 257-260.

Von Bertalanffy L., (1938) A quantitative theory of organic growth. Hum Biol 10:181–213.

Zerunian S., (2004). Pesci delle acque interne d’Italia. Ministero dell’Ambiente e Ist. Naz. Fauna

Selvatica, Quad. Cons. Natura, 20, 257 pp.

Documents

Autoecology of the marble trout - IdroLIFE...This river portion has a medium flow, alternating riffle and pools with a maximum depth of 1.8 m. The substrate is made up by sand (80%),