Three years after: What aboutThree years after: What aboutCallista chioneCallista chione restoration plans restoration plans

D. Del Piero*, M. Bolgan,* M. Burca,**, G. D. Del Piero*, M. Bolgan,* M. Burca,**, G. Calcagno,*S, D’Antoni,* C. Coglievina*, P. Calcagno,*S, D’Antoni,* C. Coglievina*, P. De Flego*, M. De Munari*,P. Diviacco***De Flego*, M. De Munari*,P. Diviacco***

•* Life Science Dept, Trieste University Italy•** ICTP,OGS, Trieste Italy•*** OGS DiamPros, Trieste Italy

C. chione C. chione emerged as alternative fishery resource soon after emerged as alternative fishery resource soon after the crisis of the crisis of C. gallina C. gallina (early 90’ties)(early 90’ties)

21 fishery vessel,equipped with hydraulic dredges are 21 fishery vessel,equipped with hydraulic dredges are involved in the exploitation in the FVG regioninvolved in the exploitation in the FVG region

It’s still the most important clam resource in Northern Italy It’s still the most important clam resource in Northern Italy (as quantities landed, 961 mt in 2008) but the price it’s not (as quantities landed, 961 mt in 2008) but the price it’s not very highvery high

The fishery management is deserved to the local “Fishermen The fishery management is deserved to the local “Fishermen Consortium” and Producers Organisation (OP) Consortium” and Producers Organisation (OP)

It’ seems a quite stupid molluscIt’ seems a quite stupid mollusc But it’s very interesting instead, because of the area coveredBut it’s very interesting instead, because of the area covered This is reflected on different growth performances in different This is reflected on different growth performances in different

areasareas

The 2007 restocking planThe 2007 restocking plan In 2007 the fishermen decided the restocking of about 20 In 2007 the fishermen decided the restocking of about 20

metric tons from a 20-22 m depth area to a “sanctuary” at metric tons from a 20-22 m depth area to a “sanctuary” at 14-16 m depth14-16 m depth

The term “sanctuary” is referred to the limitation imposed to The term “sanctuary” is referred to the limitation imposed to the fisherythe fishery

The challenge was to discover the effects of the restocking The challenge was to discover the effects of the restocking on the clamson the clams

Area overview

The fishermen Consortium, in agreement The fishermen Consortium, in agreement with OP implemented in his own district a with OP implemented in his own district a policy of fishery restriction and experimental policy of fishery restriction and experimental restocking activity, moving clams from a restocking activity, moving clams from a deeper area (20 –22 m depth) to a shallower deeper area (20 –22 m depth) to a shallower one (14-16 m depth) one (14-16 m depth)

Three years afterThree years after

A survey was done in 2010 on the A survey was done in 2010 on the restocked area and the “new” and native restocked area and the “new” and native clams were still recognizable.clams were still recognizable.

Background:Background: a difference of three years was observed a difference of three years was observed

between clams of the same length sampled between clams of the same length sampled in the two zones, the deeper being in the two zones, the deeper being apparently less favourableapparently less favourable

K-S test : D = 0.1598, Dalpha 0,05 =0,1888

sample 25-26

0

0,2

0,4

0,6

0,8

1

3 4 5 6 7 8 9

length (cm)

% c

um. F

req.

sample 25

sample 26

y = 3,0136x - 4,9148R2 = 0,9617

y = 3,3107x - 5,3516R2 = 0,9517

-1,5

-1

-0,5

0

0,5

1

1,5

1 1,2 1,4 1,6 1,8 2 2,2

2526Length-AFDW 25Length-AFDW 26

Slope test

Length-AFWD after log transformation t = 3.215, 56 DF p< 0.01

From survey done in 2010:From survey done in 2010: the cumulative frequency distributions aren’t significantly the cumulative frequency distributions aren’t significantly

differentdifferent The Length-AFDW relationships instead suggest poorer The Length-AFDW relationships instead suggest poorer

performances in restocked clamsperformances in restocked clams Benefits on recruitment were expected but till now are Benefits on recruitment were expected but till now are

lackinglacking Dedicated plancton surveys are expected to clarify the Dedicated plancton surveys are expected to clarify the

larval journey, remembering that some density-dependent larval journey, remembering that some density-dependent effect on settlement was discovered earliereffect on settlement was discovered earlier