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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

Logistic regression model results showing the probability of an individual to belong to bycatch or to landings depending on the individuals’ total length.Shows the probability of an individual to belong to bycatch (0) or to landings (1) depending on the individuals’ total length. The dashed blue line indicates the b80, the dashed grey line indicates the mean size of first maturity (Lm) of the species: (A) C. princeps (n = 112, b80 = 42.7 cm TL, Lm = 61.6 cm TL, odds ratio = 1.16); (B) P. albomaculatus (n = 112, b80 = 39.2 cm TL, Lm = 36.3 cm TL, odds ratio = 1.24); (C) P. clemensi (n = 141, b80 = 38.2 cm TL, Lm = 38.8 cm TL, odds ratio = 3.25e–7).
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fig-3: Logistic regression model results showing the probability of an individual to belong to bycatch or to landings depending on the individuals’ total length.Shows the probability of an individual to belong to bycatch (0) or to landings (1) depending on the individuals’ total length. The dashed blue line indicates the b80, the dashed grey line indicates the mean size of first maturity (Lm) of the species: (A) C. princeps (n = 112, b80 = 42.7 cm TL, Lm = 61.6 cm TL, odds ratio = 1.16); (B) P. albomaculatus (n = 112, b80 = 39.2 cm TL, Lm = 36.3 cm TL, odds ratio = 1.24); (C) P. clemensi (n = 141, b80 = 38.2 cm TL, Lm = 38.8 cm TL, odds ratio = 3.25e–7).

Mentions: The interviewed fishers’ ages ranged from 19 to 80 years, with an average of 43.0 years (SD = 11.9). While 42% of interviewed fishers were born in the Galapagos Islands, the remaining 58% were originally from mainland Ecuador. Of the 43 different species caught as bycatch, the reasons given for not landing 27 of these species was that they were not marketable species, whereas the other 14 were considered as bycatch when caught under a certain size to be marketable. Additionally, five of these species were discarded for both these reasons. Haemulidae (79%) and Serranidae (37%) were the most frequently mentioned families, represented by six and nine different species, respectively.  The most common bycatch species mentioned by fishers were A. interruptus (39%), A. scuderii (26%), E. labriformis (24%) and Sphoeroides annulatus (21%). Furthermore, 73% of fishers stated that they occasionally bycaught protected species. Of these, 68% identified sharks as bycatch with 29% of these were identified as C. galapagensis, 2% as Carcharhinus falciformes, 1% as T. obesus, while the remaining 36% did not specify the species. Rays were mentioned by 20% of fishers, turtles by 14%, sea lions by 13% and marine birds by 3% (Fig. 3). There was no significant difference between the number of species reported by fishers from the two different islands of residence based on the Pearson’s chi square test (p = 0.45).


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)

Logistic regression model results showing the probability of an individual to belong to bycatch or to landings depending on the individuals’ total length.Shows the probability of an individual to belong to bycatch (0) or to landings (1) depending on the individuals’ total length. The dashed blue line indicates the b80, the dashed grey line indicates the mean size of first maturity (Lm) of the species: (A) C. princeps (n = 112, b80 = 42.7 cm TL, Lm = 61.6 cm TL, odds ratio = 1.16); (B) P. albomaculatus (n = 112, b80 = 39.2 cm TL, Lm = 36.3 cm TL, odds ratio = 1.24); (C) P. clemensi (n = 141, b80 = 38.2 cm TL, Lm = 38.8 cm TL, odds ratio = 3.25e–7).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig-3: Logistic regression model results showing the probability of an individual to belong to bycatch or to landings depending on the individuals’ total length.Shows the probability of an individual to belong to bycatch (0) or to landings (1) depending on the individuals’ total length. The dashed blue line indicates the b80, the dashed grey line indicates the mean size of first maturity (Lm) of the species: (A) C. princeps (n = 112, b80 = 42.7 cm TL, Lm = 61.6 cm TL, odds ratio = 1.16); (B) P. albomaculatus (n = 112, b80 = 39.2 cm TL, Lm = 36.3 cm TL, odds ratio = 1.24); (C) P. clemensi (n = 141, b80 = 38.2 cm TL, Lm = 38.8 cm TL, odds ratio = 3.25e–7).
Mentions: The interviewed fishers’ ages ranged from 19 to 80 years, with an average of 43.0 years (SD = 11.9). While 42% of interviewed fishers were born in the Galapagos Islands, the remaining 58% were originally from mainland Ecuador. Of the 43 different species caught as bycatch, the reasons given for not landing 27 of these species was that they were not marketable species, whereas the other 14 were considered as bycatch when caught under a certain size to be marketable. Additionally, five of these species were discarded for both these reasons. Haemulidae (79%) and Serranidae (37%) were the most frequently mentioned families, represented by six and nine different species, respectively.  The most common bycatch species mentioned by fishers were A. interruptus (39%), A. scuderii (26%), E. labriformis (24%) and Sphoeroides annulatus (21%). Furthermore, 73% of fishers stated that they occasionally bycaught protected species. Of these, 68% identified sharks as bycatch with 29% of these were identified as C. galapagensis, 2% as Carcharhinus falciformes, 1% as T. obesus, while the remaining 36% did not specify the species. Rays were mentioned by 20% of fishers, turtles by 14%, sea lions by 13% and marine birds by 3% (Fig. 3). There was no significant difference between the number of species reported by fishers from the two different islands of residence based on the Pearson’s chi square test (p = 0.45).

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