Time spent fishing is the effort metric often studied in fisheries but it may under-represent the... more Time spent fishing is the effort metric often studied in fisheries but it may under-represent the effort actually expended by fishers. Entire fishing trips, from the time vessels leave port until they return, may prove more useful for examining trends in fleet dynamics, fisher behavior, and fishing costs. However, such trip information is often difficult to resolve. We identified ~30,000 trips made by vessels that targeted walleye pollock (Gadus chalcogrammus) in the Eastern Bering Sea from 2008-2014 by using vessel monitoring system (VMS) and landings data. We compared estimated trip durations to observer data, which were available for approximately half of trips. Total days at sea were estimated with < 1.5% error and 96.4% of trip durations were either estimated with < 5% error or they were within expected measurement error. With 99% accuracy, we classified trips as fishing for pollock, for another target species, or not fishing. This accuracy lends strong support to the use...
Deep Sea Research Part II: Topical Studies in Oceanography, 2015
ABSTRACT Changes to physical and chemical oceanographic structure can lead to changes in phytopla... more ABSTRACT Changes to physical and chemical oceanographic structure can lead to changes in phytoplankton biomass and growth, which, in-turn, lead to variability in the amount of energy available for transfer to higher trophic levels (e.g., forage fish). In general, age-0 (juvenile) walleye pollock (Gadus chalcogrammus) have been shown to have low fitness (determined by energy density and size), in warm years compared to average or cold years in the southeastern Bering Sea. Contrary to these findings, the year 2007 was a cold year with low fitness of age-0 pollock compared to the transition year of 2006 (transitioning from warm to cold conditions) and cold years, 2008–2011. In late summer/early fall (mid-August through September), significantly lower surface silicic acid concentrations coupled with low phytoplankton production and chlorophyll a (Chl a) biomass were observed in 2007 among 2006–2012 (P&lt;0.05). We postulate that the low silicic acid concentrations may be an indication of reduced surface nutrient flux during summer, leading to low primary productivity (PP). The nutrient replenishing shelf/slope water exchange that occurred during late October–February (2006–2007) indicates that deep-water nutrient/salinity reserves for the start of the 2007 growing season were plentiful and had similar concentrations to other years (2006–2012). The spring bloom magnitude appeared to be slightly below average, and surface silicic acid concentrations at the end of the spring bloom period in 2007 appeared similar to other years in the middle domain of the southeastern Bering Sea. However, during summer (June–August) 2007, high stratification and the low number of storm events resulted in low flux of nutrients to surface waters, indicated by the low surface silicic acid concentrations at the end of summer (mid-August through September). Surface silicic acid may be useful as an indicator of surface nutrient enrichment (and subsequent PP) during summer since other macronutrients (e.g. nitrate) are usually near or below detection limits at this time, and diatoms are generally scarce during summer. Surface silicic acid concentration was also positively associated with the size of juvenile fish (age-0 pollock weight and length). This reinforces the theory that nutrient availability and primary productivity are important to energy allocation for higher trophic levels during summer, and possibly provides links between stratification and wind mixing, surface nutrient input, PP and juvenile fish size and condition.
The interspecific preferences of fishes for different depths and habitats suggest fishers could a... more The interspecific preferences of fishes for different depths and habitats suggest fishers could avoid unwanted catches of some species while still effectively targeting other species. In pelagic longline fisheries, albacore (Thunnus alalunga) are often caught in relatively cooler, deeper water (>100 m) than many species of conservation concern (e.g., sea turtles, billfishes, and some sharks) that are caught in shallower water (<100 m). From 2007 to 2011, we examined the depth distributions of hooks for 1154 longline sets (3,406,946 hooks) and recorded captures by hook position on 2642 sets (7,829,498 hooks) in the American Samoa longline fishery. Twenty-three percent of hooks had a settled depth <100 m. Individuals captured in the 3 shallowest hook positions accounted for 18.3% of all bycatch. We analyzed hypothetical impacts for 25 of the most abundant species caught in the fishery by eliminating the 3 shallowest hook positions under scenarios with and without redistribution of these hooks to deeper depths. Distributions varied by species: 45.5% (n = 10) of green sea turtle (Chelonia mydas), 59.5% (n = 626) of shortbill spearfish (Tetrapturus angustirostris), 37.3% (n = 435) of silky shark (Carcharhinus falciformis), and 42.6% (n = 150) of oceanic whitetip shark (C. longimanus) were caught on the 3 shallowest hooks. Eleven percent (n = 20,435) of all tuna and 8.5% (n = 10,374) of albacore were caught on the 3 shallowest hooks. Hook elimination reduced landed value by 1.6–9.2%, and redistribution of hooks increased average annual landed value relative to the status quo by 5–11.7%. Based on these scenarios, redistribution of hooks to deeper depths may provide an economically feasible modification to longline gear that could substantially reduce bycatch for a suite of vulnerable species. Our results suggest that this method may be applicable to deep-set pelagic longline fisheries worldwide.Compensaciones entre Captura, Captura Accesoria y Valores Asentados en la Pesquera de Línea Larga de Samoa AmericanaLas preferencias interespecíficas de los peces por diferentes profundidades y hábitats sugieren que los pescadores podrían evitar capturas no deseadas de algunas especies mientras se enfocan efectivamente en otras. En las pesqueras pelágicas de línea larga, las albacoras (Thunnus alalunga) se capturan más frecuentemente en aguas relativamente más frías y más profundas (>100 m) que muchas especies de preocupación para la conservación (p. ej.: tortugas marinas, peces vela y algunos tiburones) que se capturan en aguas más someras (<100 m). De 2007 a 2011, examinamos las distribuciones de profundidad de anzuelos para 1154 conjuntos de línea larga (3, 406, 946 anzuelos) y registramos las capturas por posición de anzuelo en 2462 conjuntos (7, 829, 498 anzuelos) en la pesquería de línea larga de Samoa Americana. El 23% de los anzuelos tuvieron una profundidad establecida <100 m. Los individuos capturados en las 3 posiciones de anzuelo más someras representaron el 18.3% de toda la captura accesoria. Analizamos los impactos hipotéticos de 25 de las especies más abundantes en la pesquería al eliminar las 3 posiciones más someras de anzuelos bajo escenarios con y sin redistribución de estos anzuelos a mayores profundidades. Las distribuciones variaron por especie: 45.5% (n = 10) de las tortugas marinas (Chelonia mydas), 59.5% (n = 626) de los peces espada (Tetrapturus angustirostris), 37.3% (n = 435) de los tiburones (Carcharhinus falciformis) y 42.6% (n = 150) de otra especie de tiburones (C. longimanus) fueron capturados en los 3 anzuelos más someros. El 11% (n = 20, 435) de todo el atún y 8.5% (n = 10, 374) de albacoras fueron capturados en los 3 anzuelos más someros. La eliminación de anzuelos redujo el valor asentado por 1.6–9.2% y la redistribución de los anzuelos incrementó el promedio anual del valor asentado en relación con el status quo por 5–11.7%. Con base en estos escenarios, la redistribución de los anzuelos a mayores profundidades puede proporcionar una modificación económica factible al equipo de línea larga que podría sustancialmente reducir la captura accesoria para una cantidad de especies vulnerables. Nuestros resultados sugieren que este método puede ser aplicable a conjuntos profundos de pesquerías pelágicas de línea larga a nivel mundial.
Time spent fishing is the effort metric often studied in fisheries but it may under-represent the... more Time spent fishing is the effort metric often studied in fisheries but it may under-represent the effort actually expended by fishers. Entire fishing trips, from the time vessels leave port until they return, may prove more useful for examining trends in fleet dynamics, fisher behavior, and fishing costs. However, such trip information is often difficult to resolve. We identified ~30,000 trips made by vessels that targeted walleye pollock (Gadus chalcogrammus) in the Eastern Bering Sea from 2008-2014 by using vessel monitoring system (VMS) and landings data. We compared estimated trip durations to observer data, which were available for approximately half of trips. Total days at sea were estimated with < 1.5% error and 96.4% of trip durations were either estimated with < 5% error or they were within expected measurement error. With 99% accuracy, we classified trips as fishing for pollock, for another target species, or not fishing. This accuracy lends strong support to the use...
Deep Sea Research Part II: Topical Studies in Oceanography, 2015
ABSTRACT Changes to physical and chemical oceanographic structure can lead to changes in phytopla... more ABSTRACT Changes to physical and chemical oceanographic structure can lead to changes in phytoplankton biomass and growth, which, in-turn, lead to variability in the amount of energy available for transfer to higher trophic levels (e.g., forage fish). In general, age-0 (juvenile) walleye pollock (Gadus chalcogrammus) have been shown to have low fitness (determined by energy density and size), in warm years compared to average or cold years in the southeastern Bering Sea. Contrary to these findings, the year 2007 was a cold year with low fitness of age-0 pollock compared to the transition year of 2006 (transitioning from warm to cold conditions) and cold years, 2008–2011. In late summer/early fall (mid-August through September), significantly lower surface silicic acid concentrations coupled with low phytoplankton production and chlorophyll a (Chl a) biomass were observed in 2007 among 2006–2012 (P&lt;0.05). We postulate that the low silicic acid concentrations may be an indication of reduced surface nutrient flux during summer, leading to low primary productivity (PP). The nutrient replenishing shelf/slope water exchange that occurred during late October–February (2006–2007) indicates that deep-water nutrient/salinity reserves for the start of the 2007 growing season were plentiful and had similar concentrations to other years (2006–2012). The spring bloom magnitude appeared to be slightly below average, and surface silicic acid concentrations at the end of the spring bloom period in 2007 appeared similar to other years in the middle domain of the southeastern Bering Sea. However, during summer (June–August) 2007, high stratification and the low number of storm events resulted in low flux of nutrients to surface waters, indicated by the low surface silicic acid concentrations at the end of summer (mid-August through September). Surface silicic acid may be useful as an indicator of surface nutrient enrichment (and subsequent PP) during summer since other macronutrients (e.g. nitrate) are usually near or below detection limits at this time, and diatoms are generally scarce during summer. Surface silicic acid concentration was also positively associated with the size of juvenile fish (age-0 pollock weight and length). This reinforces the theory that nutrient availability and primary productivity are important to energy allocation for higher trophic levels during summer, and possibly provides links between stratification and wind mixing, surface nutrient input, PP and juvenile fish size and condition.
The interspecific preferences of fishes for different depths and habitats suggest fishers could a... more The interspecific preferences of fishes for different depths and habitats suggest fishers could avoid unwanted catches of some species while still effectively targeting other species. In pelagic longline fisheries, albacore (Thunnus alalunga) are often caught in relatively cooler, deeper water (>100 m) than many species of conservation concern (e.g., sea turtles, billfishes, and some sharks) that are caught in shallower water (<100 m). From 2007 to 2011, we examined the depth distributions of hooks for 1154 longline sets (3,406,946 hooks) and recorded captures by hook position on 2642 sets (7,829,498 hooks) in the American Samoa longline fishery. Twenty-three percent of hooks had a settled depth <100 m. Individuals captured in the 3 shallowest hook positions accounted for 18.3% of all bycatch. We analyzed hypothetical impacts for 25 of the most abundant species caught in the fishery by eliminating the 3 shallowest hook positions under scenarios with and without redistribution of these hooks to deeper depths. Distributions varied by species: 45.5% (n = 10) of green sea turtle (Chelonia mydas), 59.5% (n = 626) of shortbill spearfish (Tetrapturus angustirostris), 37.3% (n = 435) of silky shark (Carcharhinus falciformis), and 42.6% (n = 150) of oceanic whitetip shark (C. longimanus) were caught on the 3 shallowest hooks. Eleven percent (n = 20,435) of all tuna and 8.5% (n = 10,374) of albacore were caught on the 3 shallowest hooks. Hook elimination reduced landed value by 1.6–9.2%, and redistribution of hooks increased average annual landed value relative to the status quo by 5–11.7%. Based on these scenarios, redistribution of hooks to deeper depths may provide an economically feasible modification to longline gear that could substantially reduce bycatch for a suite of vulnerable species. Our results suggest that this method may be applicable to deep-set pelagic longline fisheries worldwide.Compensaciones entre Captura, Captura Accesoria y Valores Asentados en la Pesquera de Línea Larga de Samoa AmericanaLas preferencias interespecíficas de los peces por diferentes profundidades y hábitats sugieren que los pescadores podrían evitar capturas no deseadas de algunas especies mientras se enfocan efectivamente en otras. En las pesqueras pelágicas de línea larga, las albacoras (Thunnus alalunga) se capturan más frecuentemente en aguas relativamente más frías y más profundas (>100 m) que muchas especies de preocupación para la conservación (p. ej.: tortugas marinas, peces vela y algunos tiburones) que se capturan en aguas más someras (<100 m). De 2007 a 2011, examinamos las distribuciones de profundidad de anzuelos para 1154 conjuntos de línea larga (3, 406, 946 anzuelos) y registramos las capturas por posición de anzuelo en 2462 conjuntos (7, 829, 498 anzuelos) en la pesquería de línea larga de Samoa Americana. El 23% de los anzuelos tuvieron una profundidad establecida <100 m. Los individuos capturados en las 3 posiciones de anzuelo más someras representaron el 18.3% de toda la captura accesoria. Analizamos los impactos hipotéticos de 25 de las especies más abundantes en la pesquería al eliminar las 3 posiciones más someras de anzuelos bajo escenarios con y sin redistribución de estos anzuelos a mayores profundidades. Las distribuciones variaron por especie: 45.5% (n = 10) de las tortugas marinas (Chelonia mydas), 59.5% (n = 626) de los peces espada (Tetrapturus angustirostris), 37.3% (n = 435) de los tiburones (Carcharhinus falciformis) y 42.6% (n = 150) de otra especie de tiburones (C. longimanus) fueron capturados en los 3 anzuelos más someros. El 11% (n = 20, 435) de todo el atún y 8.5% (n = 10, 374) de albacoras fueron capturados en los 3 anzuelos más someros. La eliminación de anzuelos redujo el valor asentado por 1.6–9.2% y la redistribución de los anzuelos incrementó el promedio anual del valor asentado en relación con el status quo por 5–11.7%. Con base en estos escenarios, la redistribución de los anzuelos a mayores profundidades puede proporcionar una modificación económica factible al equipo de línea larga que podría sustancialmente reducir la captura accesoria para una cantidad de especies vulnerables. Nuestros resultados sugieren que este método puede ser aplicable a conjuntos profundos de pesquerías pelágicas de línea larga a nivel mundial.
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