Alaska Fisheries Research Articles

A comparison of acoustic backscatter between a trawling and a free-running vessel for eastern Bering Sea walleye pollock ( Theragra chalcogramma)

High-quality acoustic backscatter is continuously collected with Simrad ES-60 echosounders during the annual eastern Bering Sea (EBS) bottom trawl survey. Scientists at the Alaska Fisheries Science Center are examining the potential of combining the acoustic backscatter data collected between trawl stations with the trawl catch data to improve the precision of the survey index of walleye pollock ( Theragra chalcogramma) abundance. A previous study we conducted [von Szalay, P.G., Somerton, D.A., Kotwicki, S., 2007. Correlating trawl and acoustic data in the eastern Bering Sea: a first step toward improving biomass estimates of walleye pollock ( Theragra chalcogramma) and Pacific cod ( Gadus macrocephalus)? Fish. Res. 86, 77–83.] showed a high correlation between walleye pollock trawl catches and simultaneously collected acoustic backscatter; in this study, we compared walleye pollock acoustic backscatter collected while trawling at 3 knots with that of a free-running vessel traveling at 10 knots. Acoustic data were collected by two vessels during the 2006 and 2007 EBS bottom trawl surveys in a pair-wise fashion at 134 trawl stations. The free-running transects were conducted either immediately before or immediately after the trawl hauls and were parallel to the trawl paths but offset by approximately 250 m. The pollock acoustic backscatter was significantly greater for the trawling vessel in both the layer below the headrope and in the layer above the headrope, and was independent of the order in which the trawling and free-running transects were performed. A comparison of the seabed echo between trawling and free-running did not show a significant difference, suggesting that the discrepancy in the pollock backscatter is due to differences in fish behavior and not to differences in vessel attitude between the two operational modes. The higher backscatter values associated with trawling may be due to reactions of fish within a school that produce a coordinated swimming response, which has the potential to increase the average target strength.

First Records of the Whiteblotched Skate (Bathyraja maculata) in the Eastern Gulf of Alaska

The Whiteblotched Skate (Bathyraja maculata) is an elasmobranch species of the family Rajidae that was first described in 1977 from 21 specimens collected throughout the Bering Sea (Ishiyama and Ishihara 1977). Bathyraja maculata is distinctive, with a dorsal surface that varies from gray to dark brown and is punctuated with white to yellow blotches of various sizes. The ventral surface is white to light gray and often blotchy, darkening at the margins of the disc and on the uniformly dark tail, which has broad lateral folds. Nuchal and tail thorns are present and strongly developed, but middorsal, orbital, and scapular thorns are absent. The snout is short and flexible, and the interobital space is flat and wide (Ishiyama and Ishihara 1977; Mecklenburg and others 2002). Female B. maculata reach a maximum total length (TL) of 147 cm (Stevenson and others 2007), with males reported to a maximum size of 132 cm TL (JW Orr, National Marine Fisheries Service (NMFS), Alaska Fisheries Science Center (AFSC), Seattle, WA, pers. comm.). Bathyraja maculata ranges from the northern Sea of Japan and Sea of Okhotsk throughout the Bering Sea and Aleutian Islands (Mecklenburg and others 2002) at depths of 73 m (Fedorov 2000) to 1193 m (Stevenson and others 2007). Its easternmost record in the Aleutian Islands is off Umnak Island (53°24'N, 168041'W; Mecklenburg and others 2002). Bathyraja maculata has been commonly taken in trawl surveys of the western Bering Sea continental slope (Orlov 1998; Dolganov 1999), eastern Bering Sea continental slope (Hoff and Britt 2003, 2005) and Aleutian Islands (Zenger 2004). It also frequently occurs in shallower, continental shelf waters (ca. 100 to 200 m) of the western Bering Sea (Orlov 1998; Fedorov 2000) and Aleutian Islands (Zenger 2004), but appears to be scarce on the broad, eastern Bering Sea continental shelf (Lauth and Acuna 2007a, 2007b). Previous records of B. maculata from the Gulf of Alaska are few and restricted to the Gulf's western margin, where it has been reported at 3 locations during NMFS-AFSC bottom trawl surveys (Stevenson and others 2007, 2008; Fig. 1). The easternmost of these records represents a specimen collected approximately 163 km southwest of Kodiak Island (56°04.8'N, 156034.2'W, 191 m depth) during the summer of 1999 (DE Stevenson, NMFS-AFSC, Seattle, WA, pers. comm.). However, 3 B. maculata were recently collected from the Alexander Archipelago, southeastern Alaska, and are presented here. These records considerably extend the known distribution of B. maculata and suggest that it may be more widespread in the Gulf of Alaska than previously indicated. The Alaska Department of Fish and Game (ADFG) conducts annual longline surveys in Clarence Strait, including US waters of Dixon Entrance and Chatham Strait of the Alexander Archipelago, to assess the condition of Sablefish (Anoplopoma fimbria) stocks in these areas. Gear used during ADFG surveys consists of longlines containing forty-five 13/0 Mustad circle hooks per line, fastened at 2-m intervals and baited with squid. Twenty-five contiguous lines are deployed at established locations of 366 m depth, and gear is fished for 3 to 11 h prior to retrieval. All fishes caught during these surveys, including skates, are enumerated. Typically, only Longnose Skates (Raja rhina) are identified to species, but during the 2006 lower Clarence Strait survey, conducted from 17 to 22 May, skates of all species were distinguished. In addition, photos were taken of WINTER 2008 193

Commercial Fishing Fatalities—California, Oregon, and Washington, 2000-2006

During 2000-2006, commercial fishing was one of the most dangerous occupations in the United States, with an average annual fatality rate of 115 deaths per 100,000 fishermen. By contrast, the average annual occupational fatality rate among all U.S. workers during the same period was four deaths per 100,000 workers. During the 1990s, safety interventions in Alaska fisheries were followed by declines in that state's commercial fishing fatality rates. To assess the need for similar safety improvements in the other three Pacific Coast states, CDC analyzed data on commercial fishing fatalities from California, Oregon, and Washington during 2000-2006. The results of that analysis indicated that the three states combined had an average annual commercial fishing fatality rate of 238 deaths per 100,000 full-time equivalent (FTE) fishermen, approximately double the fishing fatality rate nationwide during the same period. CDC also determined that safety equipment (e.g., immersion suits or life rafts) had not been used adequately in these fatal events, and that the Northwest Dungeness crab fishery had the highest fatality rate of any fishery located off the coasts of California, Oregon, and Washington. To reduce fatalities among the Pacific Coast commercial fishermen at greatest risk, additional prevention measures tailored to the Northwest Dungeness crab fishery should be considered.

Integrated weight longlines with paired streamer lines – Best practice to prevent seabird bycatch in demersal longline fisheries

To evaluate a new technology – integrated weight longlines (IW) – as a viable seabird mitigation technology for demersal longline fisheries, we compared three experimental mitigation treatments, IW line alone, IW with paired streamer lines (IWPS) and unweighted longlines (UW) with PS (UWPS), to a control of no deterrent (UW alone). Trials took place on two vessels targeting Pacific cod ( Gadus macrocephalus) over a five-month period in the Bering Sea, Alaska, USA. We used multiple criteria for evaluations – catch rates of all taxa, seabird abundance and attack rate, and gear sink rate and performance – making this study the largest and most comprehensive experiment of its kind. All mitigation technologies dramatically decreased seabird bycatch rates while having little to no effect on fish catch rates. Mitigation was more effective for surface foraging seabirds ( Fulmarus glacialis and Larus spp.) than for diving seabirds (short-tailed shearwaters, Puffinus tenuirostris), reducing mortality rates by 91–100% and 80–97%, respectively. Based on multiple criteria, IWPS performed best, sinking gear within the protection of streamer lines eliminating surface forager catch completely and reducing shearwater catch by 97%, relative to the control. UWPS, status quo in the Alaska fishery, and IW alone performed similarly reducing surface forager catch rates by 98% and 91%, respectively, and shearwater rates by 87% and 80%, respectively. Seabird abundance and attack rate were poor proxies of seabird mortality, especially for IW gear. IW lines reduced the distance astern that birds have access to sinking baits by near half and its handling qualities proved superior to UW. We conclude that IW longlines and paired streamer lines are the core mitigation techniques and when deployed together, constitute the best management practice for seabird conservation in demersal longline fisheries using autoline systems.

Bomb radiocarbon age validation of Pacific ocean perch (Sebastes alutus) using new statistical methods

We used bomb-produced radiocarbon (14C) to validate ages of Pacific ocean perch ( Sebastes alutus ), which are routinely estimated with the cut-and-burn method at the Alaska Fisheries Science Center (Seattle, Washington, USA). New statistical methods to compare Δ14C in validation samples with a reference chronology are introduced: (i) calculating confidence intervals around the LOESS-smoothed Δ14C reference chronology using simultaneous inference; (ii) purposely adding biases to the validation sample ages and then analyzing the sum of squared residuals of the validation samples’ Δ14C about the LOESS-smoothed reference chronology; and (iii) standardizing the Δ14C measurements from the validation sample to better fit the reference chronology. Standardized Δ14C measurements are particularly useful when researchers suspect that environmental and biological differences between the validation samples and the reference chronology may exist that affect the level, but not the timing, of Δ14C in the samples. These new methods can be applied simultaneously. Two previous bomb radiocarbon studies on canary rockfish ( Sebastes pinniger ) and black drum ( Pogonias cromis ) were reanalyzed, further illustrating the usefulness of these new methods.

Evaluation of Video Technology for Monitoring of Multispecies Longline Catches

AbstractAt‐sea catch monitoring of the Alaskan longline fishery for Pacific halibut Hippoglossus stenolepis is insufficient. The International Pacific Halibut Commission (IPHC) conducted studies in 2002 and 2004 comparing catch composition data from electronic monitoring (EM) systems to those of at‐sea observers. The EM systems use automated data loggers linked to digital video cameras, a transducer on shipboard hydraulic systems, and a global positioning system receiver. The goal of both studies was to determine whether EM technologies could provide precise and verifiable catch composition data on commercial longline vessels to supplement and complement the data collected by fisheries observers. The EM video analyst's catch data were similar to the observers' data in the 2002 study; however, the video analyst recorded fewer fish for 7 of the 17 species categories investigated. In 2004, the IPHC employed EM technology in another study incorporating recommendations from the 2002 study, including improved camera configurations. The video analyst's data showed increased agreement with the observer data. However, the observers recorded slightly fewer individuals of some species categories, opposite the findings of the 2002 study. This change suggests that incorporating the technology recommendations enhanced the video analyst's accuracy relative to the observer data. Our analysis also highlights the fact that data provided by human observers have their own suite of errors and that the comparisons between EM and observers have no absolute standard of reference. The findings indicate that EM technology can effectively address the lack of catch composition data in the Pacific halibut and other hook‐and‐line fisheries in Alaska.

Migratory routes of short-tailed albatrosses: Use of exclusive economic zones of North Pacific Rim countries and spatial overlap with commercial fisheries in Alaska

We conducted a satellite tracking study of the endangered short-tailed albatross ( Phoebastria albatrus) to determine post-breeding season distribution, the amount of time spent within exclusive economic zones of Pacific Rim countries, and assess factors affecting spatial and temporal overlap with commercial fisheries in Alaska. We obtained 6709 locations for 14 albatrosses (131–808 locations and 51–138 days of tracking per bird). Albatrosses ranged widely throughout the North Pacific Rim, spending the majority of time within the exclusive economics zones of Japan, Russia (Kuril Islands and Kamchatka Peninsula), and the United States (Aleutian Islands and Bering Sea, Alaska). We found evidence for gender and age-related differences in distribution and, therefore, potential interaction with regional fisheries. Overall, albatrosses spent the greatest proportion of time within the Alaska exclusive economic zone. Within Alaska, albatrosses occurred most frequently in fishery management zones that encompassed the Aleutian Islands, Bering Sea, and south of the Alaska Peninsula. Short-tailed albatrosses had the greatest potential overlap with fisheries that occurred along continental shelf break and slope regions, e.g., longlining for sablefish ( Anoplopoma fimbria), where albatrosses occurred most often. Some birds, however, also made frequent excursions onto the extensive Bering Sea shelf, suggesting significant potential for interactions with the large-scale walleye pollock ( Theragra chalcogramma) and Pacific cod ( Gadus macrocephalus) fisheries. Alaskan longline fishing fleets have been proactive in using seabird deterrent devices, however, our data further emphasize that such efforts beyond the Alaska exclusive economic zone would provide a greater conservation benefit for this species.

Fish Scales: Scale and Method in Social Science Research for North Pacific and West Coast Fishing Communities

Under the Magnuson-Stevens Fishery Conservation and Management Act (MSFCMA) and other legal mandates, NOAA’s National Marine Fisheries Service (NMFS) is conducting basic social science research on fishing communities. This basic research differs from issue-driven social impact assessments in that it does not address pending policy changes or specified locations. As a consequence, NMFS’s basic social science research must cover very large geographic scales and address a broad array of analytical issues. These needs are in tension with the traditional ethnographic methods of anthropology and the MSFCMA’s focus on the community as a unit of analysis. This paper describes how anthropologists at NMFS’s Alaska Fisheries Science Center and Northwest Fisheries Science Center navigate these conflicting imperatives by adopting large-scale community profiling using social and fishing indicators informed by ethnographic site visits, and advocating a “nested-scale” analytical framework that imbricates the community le...

LASER‐METRICS OF FREE‐RANGING KILLER WHALES

Marine Mammal ScienceVolume 22, Issue 3 p. 735-743 LASER-METRICS OF FREE-RANGING KILLER WHALES J. W. Durban, J. W. Durban Alaska Fisheries Science Center, National Marine Fisheries Service, 7600 Sand Point Way NE, Seattle, Washington 98115, U.S.A. and Center for Whale Research, 355 Smuggler's Cove Road, Friday Harbor, Washington 98250, U.S.A. E-mail: john.durban@noaa.govSearch for more papers by this authorK. M. Parsons, K. M. Parsons Northwest Fisheries Science Center, National Marine Fisheries Service, 2725 Montlake Boulevard E, Seattle, Washington 98112, U.S.A. and Center for Whale Research, 355 Smuggler's Cove Road, Friday Harbor, Washington 98250, U.S.A.Search for more papers by this author J. W. Durban, J. W. Durban Alaska Fisheries Science Center, National Marine Fisheries Service, 7600 Sand Point Way NE, Seattle, Washington 98115, U.S.A. and Center for Whale Research, 355 Smuggler's Cove Road, Friday Harbor, Washington 98250, U.S.A. E-mail: john.durban@noaa.govSearch for more papers by this authorK. M. Parsons, K. M. Parsons Northwest Fisheries Science Center, National Marine Fisheries Service, 2725 Montlake Boulevard E, Seattle, Washington 98112, U.S.A. and Center for Whale Research, 355 Smuggler's Cove Road, Friday Harbor, Washington 98250, U.S.A.Search for more papers by this author First published: 09 May 2006 https://doi.org/10.1111/j.1748-7692.2006.00068.xCitations: 45Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume22, Issue3July 2006Pages 735-743 RelatedInformation

Revision of the snailfish genus Allocareproctus Pitruk & Fedorov (Teleostei: Liparidae), with descriptions of four new species from the Aleutian Islands

Liparid fishes of the genus Allocareproctus Pitruk & Fedorov were collected throughout the Aleutian Islands during surveys conducted by the Alaska Fisheries Science Center, U.S. National Marine Fisheries Service, and represent the first documented records of this genus in North America. Based on this material, we revised the genus and recognized four new species described herein. Allocareproctus is distinguished from all other liparid genera by the following characters: anterior 4–8 dorsal-fin rays with tips exserted from the fin membrane, papillae associated with some pores of the cephalic lateralis system, and symplectic extending to the medial aspects of thequadrate and metapterygoid. Allocareproctus jordani (Burke), the type species of the genus, is uniformly pink-red in coloration, with a dark peritoneum, simple teeth, a pigmented nasal papilla, and a single lobe on the orobuccal valve. It ranges from Sagami Bay, the type locality, north through the Kuril Islands, and east to Umnak Island of the Aleutian Islands, at depths of 75 to 495 m. Allocareproctus ungak n. sp. is most similar to A. jordani, differing in having trilobed teeth, an unpigmented nasal papilla, and higher counts of median-fin rays and vertebrae. It is found only between Seguam Pass and Samalga Pass in the east-central Aleutian Islands at depths of 318 to 461 m. Allocareproctus kallaion n. sp. is also known only from Seguam Pass and Samalga Pass at depths of 278 to 450 m and is distinguished from all other species of Allocareproctus by its blotchy red body color in life and dusky head coloration in life and in preservation, high gill raker count, high precaudal vertebrae count, and comb-like orobuccal valve. Allocareproctus tanix n. sp. is most similar to A. unangas n. sp. and is distinguished by its orange-peach coloration, pale peritoneum, absence of an interorbital papilla, and greater body depth. It is found only in the central Aleutians at depths of 104 to 650 m. Allocareproctus unangas n. sp. is also found only in the central Aleutians at similar depths of 210 to 465 m and is distinguished by its trilobed teeth, absence of a nasal papilla, and dark peritoneum. Based on our examination of holotypes, Careproctus pycnosoma Gilbert & Burke and C. curilanus Gilbert & Burke are valid species and not synonymous with A. jordani.

Have North Pacific killer whales switched prey species in response to depletion of the great whale populations?

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 310:235-246 (2006) - doi:10.3354/meps310235 Have North Pacific killer whales switched prey species in response to depletion of the great whale populations? Sally A. Mizroch*, Dale W. Rice National Marine Fisheries Service, Alaska Fisheries Science Center, National Marine Mammal Laboratory, 7600 Sand Point Way NE, Seattle, Washington 98115, USA *Email: sally.mizroch@noaa.gov ABSTRACT: Springer et al. (2003; Proc Natl Acad Sci USA 100:12223–12228) hypothesized that populations of seals, sea lions and sea otters in the northern North Pacific Ocean and Bering Sea declined because of increased predation by killer whales, in what they termed a ‘sequential megafaunal collapse’. They hypothesized that the killer whales had been dependent on large whales for food, and that their increased predation on the smaller marine mammals was directly due to the depletion of great whale populations as a result of post-World War II industrial whaling. The maps presented by Springer et al. (2003) masked the development and precipitous decline of post-World War II industrial whaling. Our analysis shows that north of 50°N, whaling developed slowly from 1948 to 1951, expanded steadily from 1952 to 1962, and increased very sharply from 1963 to 1967. By 1968, there was near total drop-off in catches north of 50°N as the whaling fleets moved south. Because of the extraordinary whale biomass removals in the mid-1960s, any whaling-related prey shifting should have started by 1968, not the mid-1970s as they suggested. We also present data that refute their assumption that North Pacific killer whales depended on large whales as prey either prior to or concurrent with the whaling era. During the years of the development and pulse of whaling (i.e. prior to 1968), less than 3% of the mammal-eating killer whales were observed to have large whale remains in their stomachs. Killer whales attack healthy, adult large whales only rarely, and such attacks are usually unsuccessful. Neither minke nor gray whales were depleted by post-World War II industrial whaling, and they have always been available as prey for North Pacific killer whales. KEY WORDS: Whaling · Killer whale · Sequential decline · Sequential megafaunal collapse Full text in pdf format Supplementary appendix PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 310. Online publication date: April 03, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

An Econometric Market Model for the Pacific Halibut Fishery

The Alaska and British Columbia fishery for Pacific halibut has undergone substantial restructuring over the last decade, from a regulated open-access no-holds-barred derby that largely relied on frozen inventories to satisfy market demand, to a slow-paced individual quota-based fishery that has reorganized supply chains to deliver high-quality fresh product throughout a protracted season. We have developed a simultaneous equation model of the markets for Pacific halibut and used simulations based on our model to examine: (i) linkages between harvest and revenue; (ii) ex-vessel price and revenue-induced consequences of the Alaska IFQ program; (iii) likely ex-vessel price and revenue effects of the proposed elongation of the halibut season; and (iv) potential effects of the emergence of competing supplies from halibut aquaculture.

A Rapid, High‐Throughput Technique for Detecting Tanner Crabs Chionoecetes bairdi Illegally Taken in Alaska's Snow Crab Fishery

AbstractTanner crabs Chionoecetes bairdi and snow crabs C. opilio are both important commercial species for Alaskan fisheries. The geographical ranges of Tanner and snow crabs overlap in the southeastern Bering Sea where a commercial fishery targets the more abundant snow crabs. Morphological identification of these species and of hybrids has proven difficult and impedes monitoring of the harvests. Techniques for the genetic identification of these species have been developed, but it may not be possible to process the desired number of samples because of throughput limitations and sample requirement constraints. Here we present a rapid, high‐throughput assay for identifying these species based on single nucleotide polymorphisms (SNPs) in the nuclear rRNA internal transcribed spacer 1 region and the mitochondrial DNA 16S rRNA gene. These SNPs can also be used to infer the direction of hybridization (i.e., the species of each gender).

Estimating Handling Mortality Due to Air Exposure: Development and Application of Thermal Models for the Bering Sea Snow Crab Fishery

AbstractThe fishery for snow crabs Chionoecetes opilio in Alaska occurs during the winter, and handling mortality may be high due to cold‐air exposure. Heat budget models that include convection, evaporation, long‐wave radiation, and solar radiation were developed for snow crabs. Model performance was evaluated by comparing observed and predicted temperatures of live crabs exposed to cold air. The model performed well, predicting temperatures of the body, legs, and eyes within 1.5°C. Legs and eyes cooled faster than the body and may be more susceptible to cold‐air exposure. Weather variables were ranked in the following order of importance: (1) air temperature, (2) solar radiation, (3) wind speed, (4) humidity, and (5) cloud cover. Clear, cold, breezy nights are the most detrimental conditions for crabs. Hourly weather records from a site near the fishing grounds were used in conjunction with the thermal model to estimate cooling rates for crabs every hour during actual and hypothetical seasons. The probability of damage for various cooling rates was estimated based on previously published laboratory data. Discard handling damage rates were highly variable, ranging from 0% to 30% over 21 actual fishing seasons. Damage rates for hypothetical seasons that varied in length, start day, and daily fishing hours were calculated. Damage rates were reduced by delaying the start day (15 January) until 1 March as well as by limiting fishing time to daylight hours. Combining a later starting day with limited fishing hours resulted in 90% of the hypothetical seasons having damage rates of 10% or less. Generally, longer seasons had lower damage rates, especially when fishing hours were limited. Although developed for cold‐weather Alaska fisheries, this approach can easily be adapted to other fisheries where handling mortality due to temperature changes during capture is a concern.

A framework for ecosystem impacts assessment using an indicator approach

Abstract Assessment of the historical, present, and future states of marine ecosystems and the effects that humans and climate have on the state of an ecosystem are crucial to the scientific advice required to implement an ecosystem-based fishery management system. Management of federal groundfish fisheries in Alaska considers not just the target fishery, but also the possible impact those fisheries might have on other species and the ecosystem. Management actions have ranged from providing protection of endangered species in the region to preventing new fisheries from starting on key foodweb components such as forage fish. A scientific framework for providing ecosystem-based advice that puts the ecosystem first has been evolving over the past few years. This framework provides a way of assessing ecosystem factors that influence target species, the impact the target fishery may have on associated species, and ecosystem-level impacts of fishing. An indicator approach that describes ecosystem status, and trends and measures of human and climate influence has been developed to provide advice to fishery managers. This approach is now being expanded to utilize a variety of models to predict possible future trends in various ecosystem indicators. Future implementation challenges include the refinement of these predictive models, and the inclusion of climate into the models. Identification of sensitive and meaningful ecosystem indicators is also required before a more formalized decision-making process, one that includes ecosystem considerations, can be developed. Most important, the culture of fishery management and research organizations needs to change to embrace the ecosystem-based protections already mandated by various laws.

Office of Subsistence Management and Issues and Challenges of Integrating Tek into Subsistence Fisheries Management

The intent of this article is to introduce a relatively new federal program funding social science research on fisheries in Alaska. We discuss some of the challenges of this developing applied social science program, specifically focusing on some of the issues raised by research involving the collection and analysis of traditional ecological knowledge (TEK) and its application to fisheries management in Alaska. We highlight several projects funded through the program, and close with some observations on elements of successful projects.

Quality control of age data at the Alaska Fisheries Science Center

The Alaska Fisheries Science Center operates a 14-person Age and Growth Program that specialises in the ageing of various groundfish species using otoliths. In 1983, a quality control programme was established whereby a random subsample of 20% of the total of aged samples is re-aged by a second age reader. The purpose of this programme is to assure, to the greatest extent possible, that ages used in stock assessment are based on consistent ageing criteria. This age data is entered into our AGEDATA Microsoft ACCESS™ database where it can be easily updated, corrected and analysed. VISUAL BASIC computer programmes AGREE (a precision estimating programme) and RANGES (an outlier searching programme) were written to routinely analyse age data before data are released to end-users. The statistical relationship between average percentage error and coefficient of variation is described, as well as an interpretation of Bowker’s test for symmetry. Discrepancies between the reader and tester are reconciled while viewing the problematic otoliths using a dual-headed microscope, and reconciled ages are assigned. When necessary, all questionable otoliths in a troublesome sample may be re-aged.

The effect of improved footrope contact measurements on trawl area swept estimates

Abstract Various net monitoring instruments have been used during the evolution of the Gulf of Alaska demersal trawl survey conducted by the Alaska Fisheries Science Center in an attempt to reduce haul-to-haul variability in estimates of relative density due to variation in trawl efficiency and swept area. The introduction of a bottom contact sensor greatly enhanced our ability to identify important haul events and has resulted in altered definitions of the start and end of a tow. An unintended consequence of these changed definitions is that the tow distances are longer which, in turn, has affected the time series because no corrections have been made to tow distances of hauls conducted prior to the introduction of the bottom contact sensor. The mean additional distance fished since the introduction of the bottom contact sensor was 223 m, or 8.0% of the total length of a standard 30 min haul. The challenges of correcting the time series, including differences in capture efficiencies during various stages of a tow and the need for further standardization of operating procedures are discussed.

Acoustic backscatter models of fish: Gradual or punctuated evolution

Sound-scattering characteristics of aquatic organisms are routinely investigated using theoretical and numerical models. Development of the inverse approach by van Holliday and colleagues in the 1970s catalyzed the development and validation of backscatter models for fish and zooplankton. As the understanding of biological scattering properties increased, so did the number and computational sophistication of backscatter models. The complexity of data used to represent modeled organisms has also evolved in parallel to model development. Simple geometric shapes representing body components or the whole organism have been replaced by anatomically accurate representations derived from imaging sensors such as computer-aided tomography (CAT) scans. In contrast, Medwin and Clay (1998) recommend that fish and zooplankton should be described by simple theories and models, without acoustically superfluous extensions. Since van Holliday’s early work, how has data and computational complexity influenced accuracy and precision of model predictions? How has the understanding of aquatic organism scattering properties increased? Significant steps in the history of model development will be identified and changes in model results will be characterized and compared. [Work supported by ONR and the Alaska Fisheries Science Center.]

RECONSTRUCTING SALMON ABUNDANCE IN RIVERS: AN INITIAL DENDROCHRONOLOGICAL EVALUATION

Decision-makers concerned with salmon or their stream habitats are faced with many persistent, difficult questions including: how large and variable were these populations before European settlement? Here, we examine the feasibility of reconstructing salmon abundance using links between marine nutrients carried upstream by Pacific salmon (Oncorhynchus spp.) and growth of dominant riparian trees in two Alaskan systems. We employ standard dendrochronology methods and regression models to quantify relationships between annual tree-ring growth, salmon escapement, and the climate pattern that affects oceanic production of Northeast Pacific salmon stocks, the Pacific Decadal Oscillation (PDO). We find that known, annual salmon escapement is significantly related to tree-ring growth at two sites in the Pacific coastal rainforest (PCRF) (r2 = 0.23, P < 0.05 at each site), but not at two sites in the boreal forest. We then use relationships established at PCRF sites to reconstruct preliminary salmon spawning abundances to 1820 A.D. The PDO was not correlated with local 19-yr salmon escapement records and could not be used in re- constructions. Reconstructions compare favorably to southeastern Alaska fisheries catch data from 1924 to 1994 (Pearson correlation = 0.301 (P = 0.02) and 0.401 (P < 0.01)). This study demonstrates the promise and utility of dendrochronology for reconstructing salmon returns to streams.