Goals The goals of the Alaska Fisheries Science Center (AFSC) are to work in concert with the AST... more Goals The goals of the Alaska Fisheries Science Center (AFSC) are to work in concert with the ASTWG to improve the accuracy and precision of living marine resource assessments by identifying information needs for existing and new stock assessments, identifying new and innovative uses of sampling technologies, and facilitating and conducting research to advance our understanding of the marine environment.
Towing speed on bottom trawl surveys is usually designated in terms of speed over ground (SOG) ra... more Towing speed on bottom trawl surveys is usually designated in terms of speed over ground (SOG) rather than speed through the water (STW). However, STW is likely more influential on catchability because of its more pronounced affects on trawl geometry and fish swimming speed. We conducted a 2-phase experiment to investigate: 1) the effect of STW on the footrope bottom contact of our standard survey trawl; and 2) the effect of STW on the capture efficiency of the same trawl. Speed through water was measured with a trawl-mounted current meter; distance of the footrope off-bottom was measured with a bottom contact sensor. Capture efficiency was estimated by catching the fish escaping beneath the footrope with an auxiliary net. During Phase I, bottom contact in the center of the footrope of our survey trawl was unstable at the survey towing speed of 3 knots and declined with increasing STW. At STW of 4.5 knots and above the trawl likely lifted completely off-bottom. During Phase II, capt...
The commercial fisheries for snow crab (Chionoecetes opilio) and Tanner crab (C. bairdi) in the e... more The commercial fisheries for snow crab (Chionoecetes opilio) and Tanner crab (C. bairdi) in the eastern Bering Sea are managed by using swept-area estimates of biomass (Alverson and Pereyra, 1969) provided by an annual Alaska Fisheries Science Center (AFSC) bottom trawl survey. In addition to catch and swept-area data, such biomass estimates require a value for the sampling efficiency of the trawl1 (i.e. the proportion of animals that are captured within the area spanned by the trawl doors; Dickson, 1993a). Trawl efficiency can be considered as a function of sweep efficiency (the proportion of animals within the path of the doors, bridles, and sweeps that are herded into the net path) and net efficiency (the proportion of animals that are captured within the path of the trawl net; Dickson, 1993a). For snow and Tanner crabs, owing to a lack of any contradictory evidence, sweep efficiency was assumed to be zero and net efficiency was assumed to be unity. The assumption of zero sweep e...
Absrracl The biomass of nehu (Encrusicholinu prrrpurea) in Pcarl Harbor was cstimatcd wcckly. ove... more Absrracl The biomass of nehu (Encrusicholinu prrrpurea) in Pcarl Harbor was cstimatcd wcckly. overatwoyearperiod.usinganewstockassessmen1 procedurcknownasthc Egg Production Method (EPM). Although the EPM was originally developed for assessing rclativcly long- lived, temperate anchovies (Northern Anchovy and Anchovctta). it has provcn to bc a low- cost, effective way of assessing the abundance of nehu. a short-lived. tropical stolephorid anchovy. The effectiveness of the EPM is largely the result of its bcing based on thc lifc history stage that is the least aggregated and easiest to samplc. that is. thc egg stagc. Bccausc of this, the biomass estimates obtained using the EPM are less influenced by cnvironmcntal fluctuations than estimates obtained using commercial catch statistics. Over thc study period, nehu spawning stock biomass varied between 0.5 and 5.0 tonncs and was clcarly associated with the variation in the rate of nehu bait catch for the pole-and-line tuna fishcry. Stock ...
Atka mackerel Pleurogrammus monopterygius were captured and tagged with depth and temperature rec... more Atka mackerel Pleurogrammus monopterygius were captured and tagged with depth and temperature recording devices (archival tags) on 23 July 2000 in Seguam Pass, Aleutian Islands, Alaska. Nine of the 117 tagged fish were recovered in Seguam Pass during September 2000. Fish were tagged externally just below the dorsal fin. Atka mackerel displayed strong diel behavior, with vertical movements away from the bottom occurring almost exclusively during daylight hours and little to no movement at night. Vertical movements occurred when light levels at 150 m were greater than 7.31 × 10-5 µmol photons m-2 s-1 , or approximately between 08:00 and 23:00 h Alaska Daylight Time (ADT; GMT-8) during August. Daytime vertical movements were correlated with light intensity, time of day and current velocity. The occurrence of vertical movements tended to increase with increasing light during the morning and early afternoon, but then decrease with increasing hour of the day after 13:00 h ADT. The magnitude of surface-directed vertical excursions was reduced during spring tide periods, when current velocities are highest. By comparison, the magnitude of slopedirected excursions was greater during spring tide periods and reduced during neap tide periods. Eight fish were at liberty for 42 to 44 d and 1 for 65 d. Two of the tagged males displayed nest guarding behavior for the majority of their time at liberty. Depths for these 2 males (115 to 117 m) were much deeper than previously observed for Atka mackerel spawning grounds. Given that Atka mackerel are more likely to be on the bottom during the night and less likely during the day, the variance of abundance estimates from bottom trawl surveys may be reduced by accounting for these diel differences.
... Other reproductive studies were a mixed collection of both species according to Orr & Mat... more ... Other reproductive studies were a mixed collection of both species according to Orr & Matarese (2000) (Smith, 1936; Forrester, 1969; Forrester & Thompson, 1969; Johnson et al., 1998) or were southern rock sole identified as the genus Psettichthys (Ahlstrom et al., 1984). ...
Goals The goals of the Alaska Fisheries Science Center (AFSC) are to work in concert with the AST... more Goals The goals of the Alaska Fisheries Science Center (AFSC) are to work in concert with the ASTWG to improve the accuracy and precision of living marine resource assessments by identifying information needs for existing and new stock assessments, identifying new and innovative uses of sampling technologies, and facilitating and conducting research to advance our understanding of the marine environment.
Towing speed on bottom trawl surveys is usually designated in terms of speed over ground (SOG) ra... more Towing speed on bottom trawl surveys is usually designated in terms of speed over ground (SOG) rather than speed through the water (STW). However, STW is likely more influential on catchability because of its more pronounced affects on trawl geometry and fish swimming speed. We conducted a 2-phase experiment to investigate: 1) the effect of STW on the footrope bottom contact of our standard survey trawl; and 2) the effect of STW on the capture efficiency of the same trawl. Speed through water was measured with a trawl-mounted current meter; distance of the footrope off-bottom was measured with a bottom contact sensor. Capture efficiency was estimated by catching the fish escaping beneath the footrope with an auxiliary net. During Phase I, bottom contact in the center of the footrope of our survey trawl was unstable at the survey towing speed of 3 knots and declined with increasing STW. At STW of 4.5 knots and above the trawl likely lifted completely off-bottom. During Phase II, capt...
The commercial fisheries for snow crab (Chionoecetes opilio) and Tanner crab (C. bairdi) in the e... more The commercial fisheries for snow crab (Chionoecetes opilio) and Tanner crab (C. bairdi) in the eastern Bering Sea are managed by using swept-area estimates of biomass (Alverson and Pereyra, 1969) provided by an annual Alaska Fisheries Science Center (AFSC) bottom trawl survey. In addition to catch and swept-area data, such biomass estimates require a value for the sampling efficiency of the trawl1 (i.e. the proportion of animals that are captured within the area spanned by the trawl doors; Dickson, 1993a). Trawl efficiency can be considered as a function of sweep efficiency (the proportion of animals within the path of the doors, bridles, and sweeps that are herded into the net path) and net efficiency (the proportion of animals that are captured within the path of the trawl net; Dickson, 1993a). For snow and Tanner crabs, owing to a lack of any contradictory evidence, sweep efficiency was assumed to be zero and net efficiency was assumed to be unity. The assumption of zero sweep e...
Absrracl The biomass of nehu (Encrusicholinu prrrpurea) in Pcarl Harbor was cstimatcd wcckly. ove... more Absrracl The biomass of nehu (Encrusicholinu prrrpurea) in Pcarl Harbor was cstimatcd wcckly. overatwoyearperiod.usinganewstockassessmen1 procedurcknownasthc Egg Production Method (EPM). Although the EPM was originally developed for assessing rclativcly long- lived, temperate anchovies (Northern Anchovy and Anchovctta). it has provcn to bc a low- cost, effective way of assessing the abundance of nehu. a short-lived. tropical stolephorid anchovy. The effectiveness of the EPM is largely the result of its bcing based on thc lifc history stage that is the least aggregated and easiest to samplc. that is. thc egg stagc. Bccausc of this, the biomass estimates obtained using the EPM are less influenced by cnvironmcntal fluctuations than estimates obtained using commercial catch statistics. Over thc study period, nehu spawning stock biomass varied between 0.5 and 5.0 tonncs and was clcarly associated with the variation in the rate of nehu bait catch for the pole-and-line tuna fishcry. Stock ...
Atka mackerel Pleurogrammus monopterygius were captured and tagged with depth and temperature rec... more Atka mackerel Pleurogrammus monopterygius were captured and tagged with depth and temperature recording devices (archival tags) on 23 July 2000 in Seguam Pass, Aleutian Islands, Alaska. Nine of the 117 tagged fish were recovered in Seguam Pass during September 2000. Fish were tagged externally just below the dorsal fin. Atka mackerel displayed strong diel behavior, with vertical movements away from the bottom occurring almost exclusively during daylight hours and little to no movement at night. Vertical movements occurred when light levels at 150 m were greater than 7.31 × 10-5 µmol photons m-2 s-1 , or approximately between 08:00 and 23:00 h Alaska Daylight Time (ADT; GMT-8) during August. Daytime vertical movements were correlated with light intensity, time of day and current velocity. The occurrence of vertical movements tended to increase with increasing light during the morning and early afternoon, but then decrease with increasing hour of the day after 13:00 h ADT. The magnitude of surface-directed vertical excursions was reduced during spring tide periods, when current velocities are highest. By comparison, the magnitude of slopedirected excursions was greater during spring tide periods and reduced during neap tide periods. Eight fish were at liberty for 42 to 44 d and 1 for 65 d. Two of the tagged males displayed nest guarding behavior for the majority of their time at liberty. Depths for these 2 males (115 to 117 m) were much deeper than previously observed for Atka mackerel spawning grounds. Given that Atka mackerel are more likely to be on the bottom during the night and less likely during the day, the variance of abundance estimates from bottom trawl surveys may be reduced by accounting for these diel differences.
... Other reproductive studies were a mixed collection of both species according to Orr & Mat... more ... Other reproductive studies were a mixed collection of both species according to Orr & Matarese (2000) (Smith, 1936; Forrester, 1969; Forrester & Thompson, 1969; Johnson et al., 1998) or were southern rock sole identified as the genus Psettichthys (Ahlstrom et al., 1984). ...
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