10 



Abstract — Humpback whales iMegap- 

 tera novaeangliae) are significant 

 marina consumers. To examine the 

 potential effect of predation by hump- 

 back whales, consumption (kg of prey 

 daily) and prey removal (kg of prey 

 annually) were modeled for a current 

 and historic feeding aggregation of 

 humpback whales off northeastern 

 Kodiak Island, Alaska. A current prey 

 biomass removal rate was modeled by 

 using an estimate of the 2002 hump- 

 back whale abundance. A historic 

 rate of removal was modeled from a 

 prewhaling abundance estimate (pop- 

 ulation size prior to 1926). Two pro- 

 visional humpback whale diets were 

 simulated in order to model consump- 

 tion rate. One diet was based on the 

 stomach contents of whales that were 

 commercially harvested from Port 

 Hobron whaling station in Kodiak, 

 Alaska, between 1926 and 1937. and 

 the second diet, based on local prey 

 availability as determined by fish 

 surveys conducted within the study 

 area, was used to model consumption 

 rate by the historic population. The 

 latter diet was also used to model 

 consumption by the current popula- 

 tion and to project a consumption 

 rate if the current population were to 

 grow to reach the historic population 

 size. Models of these simulated diets 

 showed that the current population 

 likely removes nearly 8.83x10*' kg 

 of prey during a 5-month humpback 

 whale feeding season, which could 

 include around 3.26 x lO*" kg of juve- 

 nile pollock (Theragra chalcogramma). 

 2.55 X 10'' kg of capelin iMalloti/s vil- 

 losiis). if these species are consumed 

 in proportion to their availability. The 

 historic humpback whale population 

 may have removed over 1.76 x 10'' kg 

 of prey annually. 



The effect of predation (current and historical) 

 by humpback whales (Megaptera novaeangliae) 

 on fish abundance near Kodiak Island^ Alaska 



Briana H. Witteveen 



Robert J. Foy 



Kate M. Wynne 



School of Fisheries and Ocean Sciences 



University of Alaska Fairbanl<s 



118 Trident Way 



KQdial<, Alaska 99615 



E-mail address (for B H Witteveen) bwideveenia'sfosuafedu 



Manuscript submitted 22 April 2004 

 to the Scientific Editor's Office. 



Manscript approved for publication 

 25 April 2005 by the Scientific Editor. 



Fish. Bull. 104:10-20 (2006). 



Numerous studies have revealed that 

 an increased awareness of trophic-level 

 interactions is essential in assessing 

 the status of complex marine ecosys- 

 tems (Overholtz et al., 1991; Hair- 

 ston and Hairston, 1993; Pascual et 

 al., 1993; Estes, 1994; Kenney et al., 

 1997; Trites et al., 1997). Such stud- 

 ies have shown that predator-prey 

 relationships in marine systems can 

 have direct and indirect effects on all 

 ecosystem members, but predictions of 

 their effects cannot be made without 

 multispecies models. 



Cetaceans are top predators in 

 marine ecosystems and consume sig- 

 nificant amounts of prey. Knowledge 

 of the distribution, abundance, and 

 foraging habits of cetaceans is, there- 

 fore, an essential element of any pe- 

 lagic ecosystem study (van Franeker, 

 1992). Many species preyed upon by 

 cetacean populations are targeted by 

 other marine predators and commer- 

 cial fisheries or are linked to fisheries 

 through complex food webs. Previous 

 studies have reported that prey re- 

 moval due to cetacean consumption 

 approaches or exceeds removals due to 

 commercial fishing (Laws, 1977; Lae- 

 vastu and Larkins, 1981; Bax, 1991, 

 Markussen et al., 1992; Nordoy et 

 al., 1995; Kenney et al., 1997). Such 

 high levels of consumption can have 

 significant effects on the distribution 

 and abundance of prey species and 

 the structure of marine communities 

 (Perez and McAlister, 1993; Kenney 

 et al., 1997; Croll et al., 1998). There- 

 fore, examining consumption by ceta- 

 ceans contributes information about 



complex ecosystem relationships and 

 the long-term sustainability of ma- 

 rine resources (Perez and McAlister, 

 1993; Kenney et al., 1997; Tamura 

 and OhsumiM. 



Humpback whales [Megaptera no- 

 vaeangliae) feed in the waters off 

 Kodiak Island and, because they are 

 considered apex predators, may in- 

 fluence the structure of the Kodiak 

 Island marine ecosystem (Fig. 1) 

 (Trites et. al., 1997; Croll et. al., 

 1998). Modeling the amount of prey 

 consumed (kg of prey annually) by 

 feeding humpback whales is, there- 

 fore, a useful tool for evaluating their 

 role as marine predators. 



Cetaceans, in general, are described 

 as opportunistic in their food selec- 

 tion, although species tend to select 

 broad categories of prey such as 

 cephalopods, fish, or zooplankton (To- 

 milin, 1954; Nemoto, 1959; Klumov, 

 1966; Sigurjonsson and Vikingsson, 

 1998). Humpback whales are clas- 

 sified as generalists and target a 

 wide variety of prey species (Nemoto, 

 1970; Perry et al., 1999). They have 

 been shown to be seasonal feeders on 

 euphausiids [Thysanoessa spp.) and 

 schooling fish species up to 30 cm in 

 length, including capelin (Mallotus 

 villosus). Pacific herring iClupea pal- 



1 Tamura, T., and S. Ohsumi. 2000. Re- 

 gional assessments of prey consumption 

 by marine cetaceans in the world. In- 

 ternational Whaling Commission docu- 

 ment SC/52/E6, 45 p. Website: www. 

 icrwhale.org/eng/SC52E6.pdf [Accessed 

 on 30 November 20021. 



