Alaska Fishery Research Bulletin Issues, Vol.8 No. 2 - Winter 2001

Trawl Comparisons of Fishing Power Differences and Their Applicability to National Marine Fisheries Service and Alaska Department of Fish and Game Trawl Survey Gear

Paul G. von Szalay and Eric Brown- Vol. 8(2):85-95. 2001.

We analyzed catch per unit effort data collected near Kodiak Island during a side-by-side trawl comparison experiment between the National Marine Fisheries Service (NMFS) and the Alaska Department of Fish and Game (ADF&G) conducted in 1997. Using Kappenman’s estimator, fishing power correction factors (FPCs) were estimated for 4 common species, and a mean squared error-based decision rule to determine whether the use of fishing power correction factors is warranted was applied in each case. The NMFS vessel–gear unit was considerably more efficient at catching walleye pollock Theragra chalcogramma (FPC = 3.84) and Pacific cod Gadus macrocephalus (FPC = 1.72) than its ADF&G counterpart, but the ADF&G vessel–gear unit was somewhat more efficient at catching arrowtooth flounders Atheresthes stomias (FPC = 0.73) and flathead sole Hippoglossoides elassodon (FPC = 0.75). The outcome of the decision rule suggests that fishing power correction factors should be applied for all 4 species when integrating the 2 agencies’ survey data. Length-based FPCs, designed to fine-tune fishing power corrections to individual size categories, were not significantly different for Pacific cod (P = 0.91), arrowtooth flounder (P = 0.096), or flathead sole (P = 0.15). However, 3 significantly different length-based FPCs were obtained for walleye pollock (0–14 cm, 15–62 cm, and > 62 cm).

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Summer Zooplankton Abundance and Composition Estimates from 20-m Vertical Hauls in Prince William Sound, Alaska, Using Three Net Meshes

Molly V. Sturdevant- Vol. 8(2):96-106. 2001.

The abundance and composition of mesozooplankton in the top 20 m of the water column were compared between NORPAC nets having 105-, 243- and 303-µm meshes to evaluate net retention and gear suitability for sampling prey fields of age-0 and age-1 forage fish. Single, consecutive vertical hauls were made with each net in daylight at 3 stations in northeastern Prince William Sound, Alaska, on August 5–6, 1995. Individual samples were examined microscopically, and data were pooled by mesh size for analysis. Total zooplankton abundance differed by an order of magnitude between 105- and 303-µm mesh nets (41,000 and 1,400 organisms·m-3). Small calanoid copepods comprised equal to or less than 86% of the composition in all the net mesh sizes. Net retention in the smallest meshes was significantly higher for the small species and stages of calanoids and for several other small taxa (bivalve larvae, invertebrate eggs, barnacle larvae) compared to the largest mesh; conversely, retention for chaetognaths was significantly higher in the largest mesh. The 105-µm mesh net best represented abundances and composition of mesozooplankton consumed by forage fish in summer, predominantly small calanoids, because the others undersampled taxa present in the diets of Pacific herring Clupea pallasi, pink salmon Oncorhynchus gorbuscha, walleye pollock Theragra chalcogramma, Pacific tomcod Microgadus proximus, capelin Mallotus villosus, and Pacific sand lance Ammodytes hexapterus. Although sampling gear bias has long been recognized as critical to estimates of zooplankton production and community structure, this study demonstrates the importance of selecting the appropriate sampling net mesh to characterize prey selection and consumption by planktivorous fish.

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A Survey of Participants in the Lower and Central Cook Inlet Halibut and Salmon Sport Fisheries

Mark Herrmann, S. Todd Lee, Keith R. Criddle, and Charles Hamel- Vol. 8(2):107-117. 2001.

Results of a postal survey of participants in the 1997 central and lower Cook Inlet saltwater halibut and salmon sport fisheries are reported and compared with the results of the 1997 Alaska Department of Fish and Game (ADF&G) statewide sportfishing harvest survey and the 1998 ADF&G saltwater charter vessel logbook census. Despite the use of different survey methods and instruments, responses to related questions correspond closely across all 3 surveys. Nonresident sportfishing accounted for 44% of the 197,556 angler-days of effort in the lower and central Cook Inlet halibut and salmon saltwater sport fisheries during 1997. Effort levels by Kenai Peninsula Borough residents and other Alaskans were 25% and 31% of the total, respectively. Local residents, other Alaskans, and nonresidents exhibited differing demographic and economic characteristics and different catch rates, selected different fishing modes, and incurred different trip expenditures. Alaskan respondents were younger, lived with larger families, and had a lower average income than the average nonresident angler. Women comprised over a third of the Alaskan anglers, but scarcely more than a fifth of the nonresidents. Nonresidents, local residents, and other Alaskans accounted for 65%, 10%, and 25% of the charter client-days, respectively. Nonresidents incurred higher average fishing trip-specific costs than residents for similar trips. Likewise, fishing trip-specific expenditures were higher for charter clients than for private-vessel or shorebased fishers. Although 88% of the Alaskan respondents identified saltwater fishing as the primary purpose of their trip to the Kenai Peninsula, 57% of the nonresident respondents indicated their participation was incidental to their primary trip purpose. After adjusting for spending that would have occurred in the absence of sportfishing, we estimate that $34.1 million in expenditures can be uniquely attributed to the 1997 central and lower Cook Inlet halibut and salmon sport fisheries. These expenditures include $24.9 million in “new” money, money released into the Kenai Peninsula economy by individuals who reside outside the borough. These same fisheries contributed $22.3 million and $23.5 million in new money in 1998 and 1999, respectively.

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Macrocystis Biomass, Quality, and Harvesting Effects in Relation to the Herring Spawn-On-Kelp Fishery in Alaska

Peter G. van Tamelen and Doug Woodby- Vol. 8(2):118-131. 2001.

Giant kelp Macrocystis spp. is harvested for use in herring spawn-on-kelp, also called roe-on-kelp, fisheries, but information on the biology and ecology of kelp is limited for Southeast Alaska. A successful management plan must evaluate both the amount of kelp available for harvest and the recovery rates of kelp from harvest. In this study, estimating the amount of kelp available consisted of first estimating the total abundance of kelp in a survey area and second estimating the biomass of available and desirable kelp. The total biomass was estimated by surveying the surface area of kelp beds in selected regions on the west coast of Prince of Wales Island. Randomly selected “index beds” were surveyed to determine kelp density, and samples were measured and weighed to estimate the average weight of kelp fronds. About 2.04 x 105 t of kelp were identified in the survey. The harvest of kelp for spawn on kelp is highly selective. We found that blades at least 14 cm wide and fronds with a high proportion of desirable blades were selected. The proportion of blades and fronds meeting these selection criteria were determined for the index beds, and the biomass of desirable kelp was estimated to be about 14% of the total kelp biomass in April. The growth in kelp canopy was rapid from March to April, with April canopies about 82% larger than March canopies. Even if kelp harvests increase 10 times over present levels, the harvest will represent only about 4.5% of the total estimated amount of kelp. Experimentally harvesting kelp canopies in March, April, or at both times had few significant effects. Kelp beds that were experimentally harvested at both times or only in April had shorter fronds and possibly fewer large fronds and fronds per plant. This experiment was monitored only one month after the last harvest, so there may not have been sufficient time for the cut kelp to recover.

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Effects of Temperature on Length of Intermolt Periods in Juvenile Male Chionoecetes bairdi

A. J. Paul and J. M. Paul - Vol. 8(2):132-134. 2001.

The purpose of this study was to examine the effect of temperature on the intermolt duration of juvenile Tanner crabs Chionoecetes bairdi Rathbun. The average length of the intermolt period for Gulf of Alaska male Tanner crabs, with carapace widths (CW) of 24–26 mm, was ascertained for captives held at 3°, 6°, and 9°C. No test specimens died, and regardless of rearing temperature they fed avidly during captivity. Molting intervals were summarized in units of days and degree days. Increasing the rearing temperature from 3° to 6°C reduced the number of days between molts, but raising it to 9°C did not result in a similar reduction. The intermolt periods were 154 (SD =24), 78 (SD = 14), and 74 (SD = 8) days for juveniles held at 3°, 6°, and 9°C, respectively. The number of days between molts for the 3°C test group was significantly longer than the intermolt duration of juveniles reared at 6° and 9°C. There was no significant difference in the number of days between molts for the 6° and 9°C groups. In units of degree days, the mean intermolt periods at 3° and 6°C were nearly identical: 462 (SD = 74) and 467 (SD = 87) days, respectively. At 9°C molting occurred after an average of 665 (SD = 73) degree days. At 3° and 6°C, degree-day intermolt durations were not significantly different, but at 9°C the intermolt duration was significantly longer than those observed at 3° and 6°C. Thus, at 9°C, a temperature commonly encountered by Gulf of Alaska Tanner crabs during fall, a prolonging of the degree-day intermolt duration occurred. The degree-day method of describing intermolt durations worked adequately at 3° and 6°C, but above 6°C additional experiments are needed to better comprehend the influence of temperature on molting frequency. There was no obvious relationship between rearing temperature and growth. The average increase in carapace width for males held at 3°, 6°, and 9°C was 33% (SD = 4), 32% (SD = 6), and 32% (SD = 8) with no significant differences detected in growth per molt relative to rearing temperature.

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Growth of Juvenile Golden King Crabs Lithodes aequispinus in the Laboratory

A. J. Paul and J. M. Paul - Vol. 8(2):135-138. 2001.

Growth observations were made for juvenile male golden king crabs Lithodes aequispinus with carapace lengths (CL) of 2 to 35 mm to improve our understanding of the recruitment process. Gravid females were captured in Prince William Sound, Alaska, and juveniles were reared in the laboratory at 3°–10°C to obtain information on growth per molt and intermolt duration. The equation describing the increase in CL for crabs 2 to 35 mm CL was: New CL mm = Initial CL (1.25) + 0.14; r2 = 0.99, n = 76. The average increase in CL after molting was 28% (SD = 8%), and the corresponding value for chela height (CH) was 33% (SD = 17%). The intermolt duration, in units of degree days, of crabs 2 to 35 mm CL was described by the equation: Intermolt Duration = Initial CL mm (16.32) + 259; r2 = 0.76. The results from this study provide new insight into the growth patterns of this commercially important species.

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