[MARMAM] Biomass removal by dolphins and fisheries in a Mediterranean Sea coastal area: Do dolphins have an ecological impact on fisheries?

Giovanni Bearzi giovanni.bearzi at gmail.com
Mon May 3 02:56:58 PDT 2010


The following article has just become available online:


Biomass removal by dolphins and fisheries in a Mediterranean Sea coastal
area: 
do dolphins have an ecological impact on fisheries?

Bearzi G., Agazzi S., Gonzalvo J., Bonizzoni S., Costa M., Petroselli A.
2010. 

Aquatic Conservation: Marine and Freshwater Ecosystems. DOI:
10.1002/aqc.1123

ABSTRACT

1. Dolphins are often claimed to compete with fisheries, including through
removal of substantial biomass. To calculate the biomass removed by
fisheries and the degree of resource overlap with dolphins in a coastal area
of Greece, estimates of dolphin abundance based on photographic
capture-recapture were combined with an assessment of fishing effort and
catch.

2. The estimated total biomass consumed annually by local dolphin
populations - 15 short-beaked common dolphins and 42 common bottlenose
dolphins - was 15.5 and 89.8 tonnes, respectively. The total biomass removed
by the local fishing fleet (307 fishing boats) was 3469.2 tonnes, i.e. about
33 times greater than that removed by dolphins.

3. Dolphins removed 2.9% of the total biomass, fisheries 97.1%. Nine purse
seiners (representing only 3% of the active fishing fleet) were responsible
for 31.9% of biomass removal. Similarity of biomass composition between
dolphins and fisheries was expressed by a Pianka index of 0.46 for common
dolphins and 0.66 for bottlenose dolphins.

4. Overlap differed according to fishing gear. Common dolphin overlap was
higher with purse seiners (0.82), and lower with beach seiners (0.31),
bottom trawlers (0.11) and trammel boats (0.06). There was virtually no
overlap with longliners (0.02). Bottlenose dolphin overlap was higher with
trammel boats (0.89) and bottom trawlers (0.75), and lower with longliners
(0.38), purse seiners (0.24) and beach seiners (0.18). There was minimal
overlap (0.12) between the two dolphin species.

5. This study suggests that ecological interactions between dolphins and
fisheries in this coastal area have minor effects on fisheries. Conversely,
prey depletion resulting from overfishing can negatively affect dolphins.
Fisheries management measures consistent with national and EU legislation
are proposed.

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A pdf copy can be obtained from the journal's web site:

http://www3.interscience.wiley.com/journal/123394774/abstract

or from me:

giovanni.bearzi at gmail.com

_____________________________________________________
Giovanni Bearzi, Ph.D.

President, Tethys Research Institute
Viale G.B Gadio 2, 20121 Milano, Italy
http://www.tethys.org/giovanni_bearzi.htm
http://www.tethys.org/
_____________________________________________________


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