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Catch, bycatch and discards of the Galapagos Marine Reserve small-scale handline fishery.

Zimmerhackel JS, Schuhbauer AC, Usseglio P, Heel LC, Salinas-de-León P - PeerJ (2015)

Bottom Line: Even though there are indications that the small-scale handline fishery of the Galapagos Marine Reserve has a low selectivity, information on its bycatch has never been published.We used onboard monitoring and interview data to assess the bycatch of the Galapagos handline fishery by estimating the bycatch ratio, determining species compositions of landings and bycatch, identifying fishers' reasons for discarding certain individuals, and revealing historical trends in the bycatch ratio.Most individuals were not landed for economic motivations, either because species (77.4%) or sizes (17.7%) are unmarketable or for regulatory reasons (5.9%).

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Marine Science, Charles Darwin Research Station , Puerto Ayora, Galapagos Islands , Ecuador.

ABSTRACT
Fisheries bycatch is a significant marine conservation issue as valuable fish are wasted and protected species harmed with potential negative ecological and socio-economic consequences. Even though there are indications that the small-scale handline fishery of the Galapagos Marine Reserve has a low selectivity, information on its bycatch has never been published. We used onboard monitoring and interview data to assess the bycatch of the Galapagos handline fishery by estimating the bycatch ratio, determining species compositions of landings and bycatch, identifying fishers' reasons for discarding certain individuals, and revealing historical trends in the bycatch ratio. The estimated bycatch ratio as a function of biomass of 0.40 and a diverse species composition of target catch and bycatch confirmed the low selectivity of this fishery. Most individuals were not landed for economic motivations, either because species (77.4%) or sizes (17.7%) are unmarketable or for regulatory reasons (5.9%). We found that bycatch contributes to growth overfishing of some target species because they are discarded or used as bait before reaching their first maturity. Moreover, over half of interviewees perceived a historical decrease in bycatch ratios that was explained by a diversification of the target catch due to the reduction in abundance of the traditionally most important target species. As some target species show signs of overfishing and to date there are no specific regulations for the finfish fishery species in place, we recommend the implementation of a series of management measures to protect critical life stages of overexploited species and to improve the selectivity of the Galapagos handline fishery.

No MeSH data available.


Related in: MedlinePlus

Percentage of responses of interviewees (n = 100) for each mentioned taxa as well as the reasons of fishers to not land these taxa.Reasons to not land taxa are unmarketable species (dark blue), unmarketable size (light blue) and regulatory discard (green).
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fig-4: Percentage of responses of interviewees (n = 100) for each mentioned taxa as well as the reasons of fishers to not land these taxa.Reasons to not land taxa are unmarketable species (dark blue), unmarketable size (light blue) and regulatory discard (green).

Mentions: The species P. albomaculatus, C. princeps and P. Clemensi were not only some of the most important target species in landings, they also were some of the most frequently caught bycatch species. Those three species made up five, four and two percent of all bycatch biomass, respectively. The biomass of C. princeps was mostly landed (79%), but partly used as bait (19.6%), partly discarded dead (1.2%) and to a small extent discarded alive (0.6%). Of the total biomass of P. albomaculatus, 76% was landed, 16.1% was used as bait, 8.0% discarded dead and only 0.9% was discarded alive. Finally, 75% of the caught biomass of P. clemensi was landed, 22.7% used as bait and 2.1% was discarded. No individuals of this species were discarded alive. An adequate sample size (n ≥ 100) for these three species allowed us to apply a logistic regression model which predicted the size below which individuals have a 80% chance to become bycatch. Results of this model are indicated in Fig. 4.


Catch, bycatch and discards of the Galapagos Marine Reserve small-scale handline fishery.

Zimmerhackel JS, Schuhbauer AC, Usseglio P, Heel LC, Salinas-de-León P - PeerJ (2015)

Percentage of responses of interviewees (n = 100) for each mentioned taxa as well as the reasons of fishers to not land these taxa.Reasons to not land taxa are unmarketable species (dark blue), unmarketable size (light blue) and regulatory discard (green).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4465951&req=5

fig-4: Percentage of responses of interviewees (n = 100) for each mentioned taxa as well as the reasons of fishers to not land these taxa.Reasons to not land taxa are unmarketable species (dark blue), unmarketable size (light blue) and regulatory discard (green).
Mentions: The species P. albomaculatus, C. princeps and P. Clemensi were not only some of the most important target species in landings, they also were some of the most frequently caught bycatch species. Those three species made up five, four and two percent of all bycatch biomass, respectively. The biomass of C. princeps was mostly landed (79%), but partly used as bait (19.6%), partly discarded dead (1.2%) and to a small extent discarded alive (0.6%). Of the total biomass of P. albomaculatus, 76% was landed, 16.1% was used as bait, 8.0% discarded dead and only 0.9% was discarded alive. Finally, 75% of the caught biomass of P. clemensi was landed, 22.7% used as bait and 2.1% was discarded. No individuals of this species were discarded alive. An adequate sample size (n ≥ 100) for these three species allowed us to apply a logistic regression model which predicted the size below which individuals have a 80% chance to become bycatch. Results of this model are indicated in Fig. 4.

Bottom Line: Even though there are indications that the small-scale handline fishery of the Galapagos Marine Reserve has a low selectivity, information on its bycatch has never been published.We used onboard monitoring and interview data to assess the bycatch of the Galapagos handline fishery by estimating the bycatch ratio, determining species compositions of landings and bycatch, identifying fishers' reasons for discarding certain individuals, and revealing historical trends in the bycatch ratio.Most individuals were not landed for economic motivations, either because species (77.4%) or sizes (17.7%) are unmarketable or for regulatory reasons (5.9%).

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Marine Science, Charles Darwin Research Station , Puerto Ayora, Galapagos Islands , Ecuador.

ABSTRACT
Fisheries bycatch is a significant marine conservation issue as valuable fish are wasted and protected species harmed with potential negative ecological and socio-economic consequences. Even though there are indications that the small-scale handline fishery of the Galapagos Marine Reserve has a low selectivity, information on its bycatch has never been published. We used onboard monitoring and interview data to assess the bycatch of the Galapagos handline fishery by estimating the bycatch ratio, determining species compositions of landings and bycatch, identifying fishers' reasons for discarding certain individuals, and revealing historical trends in the bycatch ratio. The estimated bycatch ratio as a function of biomass of 0.40 and a diverse species composition of target catch and bycatch confirmed the low selectivity of this fishery. Most individuals were not landed for economic motivations, either because species (77.4%) or sizes (17.7%) are unmarketable or for regulatory reasons (5.9%). We found that bycatch contributes to growth overfishing of some target species because they are discarded or used as bait before reaching their first maturity. Moreover, over half of interviewees perceived a historical decrease in bycatch ratios that was explained by a diversification of the target catch due to the reduction in abundance of the traditionally most important target species. As some target species show signs of overfishing and to date there are no specific regulations for the finfish fishery species in place, we recommend the implementation of a series of management measures to protect critical life stages of overexploited species and to improve the selectivity of the Galapagos handline fishery.

No MeSH data available.


Related in: MedlinePlus