559 



Abstract— Wo analyzed data from Na- 

 tional Marine Fisheries Service bottom 

 trawl surveys carried out triennially 

 from 1984 to 1996 in the Gulf of Alaska 

 iGOA).The continental shelf and upper 

 slope (0-500 m) of the GOA support a 

 rich demersal fish fauna dominated 

 by arrowtooth flounder ^Atheresthes 

 stomias), walleye pollock (Theragra 

 chalcogrammaK Pacific cod iGadus 

 macrocephalus). Pacific halibut (Hip- 

 poglossus stenolepis). and Pacific Ocean 

 perch [Sebastes atutus). Average catch 

 per unit of effort (CPUE) of all ground- 

 fish species combined increased with 

 depth and had a significant peak near 

 the shelf break at 150-200 m. Species 

 richness and diversity had significant 

 peaks at 200-300 m. The western GOA 

 was characterized by higher CPUEs 

 and lower species richness and diversity 

 than the eastern GOA. Highest CPUEs 

 were observed in Shelikof Strait, along 

 the shelf break and upper slope south 

 of Kodiak Island, and on the banks 

 and in the gullies northeast of Kodiak 

 Island. Significant differences in total 

 CPUE among sur%'eys suggest a 40*7^ 

 increase in total groundfish biomass 

 between 1984 and 1996. A multivariate 

 analysis of the CPUE of 72 groundfish 

 taxa revealed strong gradients in spe- 

 cies composition with depth and from 

 east to west, and a weak but signifi- 

 cant trend in species composition over 

 time. The trend over time was associ- 

 ated with increases in the frequency 

 of occurrence and CPUE of at least 

 eight taxa, including skates (Rajidae), 

 capelin iMallotus villosus), three flat- 

 fish species, and Pacific Ocean perch, 

 and decreases in frequency of occur- 

 rence and CPUE of several sculpin 

 (Myoxocephalus spp. I species. Results 

 are discussed in terms of spatial and 

 temporal patterns in productivity and 

 in the context of their ecological and 

 management implications. 



Spatial and temporal patterns In the 

 demersal fish community on the shelf and 

 upper slope regions of the Gulf of Alaska 



Franz J. Mueter 

 Brenda L. Norcross 



Institute of Marine Science 



University of Alaska Fairbanks 



PC Box 757220 



Fairbanks, Alaska 99775-7220 



Present address (lor F J Mueter): 697 Fordham Drive 



Fairbanks, Alaska 99709 

 E-mail address (for F J. Mueter):fmueteriS'mosquitonet-Com 



Manuscnpt accepted 22 March 2002. 

 Fish. Bull. 100:559-581 (2002i. 



The continental shelf and upper slope of 

 the Gulf of Alaska (GOA, Fig. 1) support 

 a diverse community of demersal fishes. 

 This community includes many com- 

 mercial species that support rich bottom 

 trawl and longline fisheries with land- 

 ings averaging approximately 250,000 

 metric tons per year over the past two 

 decades (NPFMCM. The commercially 

 most important species during the past 

 decade have been walleye pollock iTher- 

 agra chalcogramma). Pacific halibut 

 iHippoglossus stenolepis). Pacific cod 

 {Gadus macrocephalus), other flatfish 

 species (Pleuronectidae), rockfish (Se- 

 bastes spp. ), and sablefish (Anoplopoma 

 fimbria). Arrowtooth flounder iAtheres- 

 thes stomias), although currently the 

 dominant demersal species by biomass, 

 is a minor component of total landings. 

 Triennial bottom trawl surveys have 

 been carried out since 1984 to assess 

 the abundance and distribution of 

 the main commercial species in the 

 GOA (Martin, 1997). The surveys also 

 provide data on noncommercial fish 

 species and other associated benthic 

 megafauna. At least 140 species of 

 fishes belonging to 33 families were 

 collected during the 1996 GOA bottom 

 trawl survey (Martin, 1997). Rockfish 

 (Scorpaenidae) were the best repre- 

 sented family with 25 species, followed 

 by sculpins (Cottidae, 24 species) and 

 flatfishes (Pleuronectidae, 16 species). 

 Data from similar bottom trawl sur- 

 veys have been used to investigate the 

 ecology and zoogeography of fish as- 

 semblages in many parts of the world, 

 including the North Pacific (Gabriel 



and Tyler, 1980; Rogers and Pikitch, 

 1992; Jay, 1996). However, to our 

 knowledge there have been no studies 

 in which demersal fish assemblages 

 from the GOA shelf and slope were 

 examined. 



To understand, and eventually to 

 predict, the effects of environmental 

 variations on fish stocks, scientists 

 and managers increasingly advocate 

 ecosystem approaches to research and 

 management (Yaffee et al. , 1996; Lang- 

 ton and Haedrich, 1997). Ecosystem 

 management must be based on mul- 

 tispecies relationships and overcome 

 the current focus on individual spe- 

 cies (Langton and Haedrich, 1997). An 

 important prerequisite for successful 

 multispecies approaches is an under- 

 standing of the species structure offish 

 communities in space and time. 



The purpose of this paper is to iden- 

 tify spatial and temporal patterns in 

 the composition of the demersal fish 

 community from the GOA. Specific 

 objectives are 1) to identify the main 

 environmental and spatial gradients 

 along which the groundfish community 

 is structured, and 2) to identify long- 

 term changes in the composition of the 

 groundfish community. 



1 NPFMC (North Pacific Fisheries Man- 

 agement Council). 1997. Stock assess- 

 ment and fishery evaluation report for 

 the groundfish resources of the Gulf of 

 Alaska. North Pacific Fisheries Manage- 

 ment Council, 605 West 4th Ave., Suite 

 306, Anchorage, AK 99501. 



