The status of basking sharks in the South-WestTom HortonCornwall Wildlife Trust and Marine DiscoveryE: [email protected] Southwest is viewed as the UK’s principal ‘hotspot’ for the world’s second largest fish. Sightings of basking sharks in shoals of up to 80 individuals have previously been relatively commonplace, and these ocean giants are strongly associated with the region during the summer months. A multitude of datasets detailing basking shark abundance exist in the Southwest and all, despite differences in sampling protocols, show a marked decline in basking shark abundance in previous years. This presentation will focus on effort-based data collected by Marine Discovery (2007-2014) detailing this recent decline, but will also comment on trends observed in other datasets collected by Seawatch Southwest, Cornwall Wildlife Trust, the Marine Conservation Society and the Shark Trust. This is the first stage of a broader-scale project that seeks to elucidate environmental drivers behind observed trends.Furthermore, the presentation will highlight the importance of long-term public recording datasets and comment on how Seaquest Southwest – Cornwall Wildlife Trust’s public sightings scheme, aims to focus survey effort in order to better monitor regional mobile species’ hotspots.
Citation preview
The status of basking
sharks in Cornwall
Tom Horton
The Project
Previous works suggesting decline in numbers
Following another "interesting year . . .
Long-term aim is to categorise and understandlong-term trends in
abundance
Work in progress . . .
Overview
Basking sharks in the UK and Cornwall
2014
Long-term trends
Implications
The future
BASKING SHARKS
IN THE UK
Seasonal visitors
Fished 1946-1997
Wildlife and Countryside Act (1981)
Listed on CITES & CMS
Vulnerable IUCN Red List (1996-)
SW England regional hotspot
Witt et.al., 20
12
BASKING SHARKS
IN CORNWALL
ICONIC species
Synonymous with Porthcurno& Sennen
Income through wildlife tour operators
Multiple sightings programs
Proposed to be listed in MCZs
How about numbers?
2014
01
2
3
4
5
6
7
8
9
10Independent UoE Project
2014 totals
59 records
91 sharks
1998 - 2014 average
273 records
1226 sharks
Record
s
Map to show shark locations on 4.5.2014
4.5.2014
4.5.2014
59 records comprising 91 sharks
Mostly South coast
No large shoals
60% of records 23.4.2014-7.5.2-2014
Long-term trends
1997- present1988- present 1997- present
2007- present2007- 2011
1. Public recording
2. Effort-based
2008 - 2012
Long-term trends
1997- present1988- present 1997- present
2007- present2007- 2011
1. Public recording
2. Effort-based
2008 - 2012
Seawatch Southwest
Marine Discovery
547
221194
218
1459
115
13
0
100
200
300
400
500
600
0
5
10
15
20
25
30
35
40
2007 2008 2009 2010 2011 2012 2013 2014
March
April
May
June
July
August
Sept
Oct
Nov
Sharks
SWSWS
hark
s h
-1
Sh
ark
s y
ea
r-1
Shark
s 1
00km
-1
Sh
ark
s y
ea
r-1
Yearly average:156 sharks
MDYearly average:
173 sharks
458
209
51 4713
0
50
100
150
200
250
300
350
400
450
500
0
0.1
0.2
0.3
0.4
0.5
0.6
2007 2008 2009 2010 2011
July
August
Sept
Oct
Sharks
Sh
ark
s y
ea
r-1
JuneSept
Cornwall Wildlife Trust
1711
2200
728
13851219
599
317
786
2929
4001
1607
1069
796
77
1050
28391
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0
50
100
150
200
250
300January
February
March
April
May
Reco
rds
Sh
ark
s y
ea
r-1
SWSW & MD Start
So what is this telling us?
Shark sightings have declined in the SW
1. Species assemblage
change
2. Zooplankton density
3. Temperature
Calanus helgolandicus @
L4
0.00
50.00
100.00
150.00
200.00
250.00
300.00
350.00
400.00
450.00
MD 2013 peak CWT 2014 peak
Ind
ivid
ua
ls m
3
Data courtesy of Rachel Harmer @ PML
basking shark status
CWT dataset shows periodicity +/-
SWSW & MD show decline -
A need for the inclusion of long-term prey and SST data
Sub-surface sharks?
Importance of monitoring schemes
Moving Forwards
Summary
Raw data show a decline in sightings since 2006/07
Combined effects of SST & prey rather than a population
decline
