Burkett 



Chapter 22 



Food Habits and Prey Ecology 



and landings have decreased. Simultaneously, there was a 

 decrease in consumption of sand eels by seabirds. These 

 findings indicate that the switching of seabirds from sand 

 eels to other prey is in approximate proportion to the 

 abundance of sand eels. However, Bailey and others (1991) 

 concluded that more data were needed to significantly refine 

 the analysis. It was noted that different seabirds respond 

 differently to changes in stock. Surface feeders must forage 

 close to the colony and make many fishing trips per day; 

 thus they are especially sensitive to reduction in food 

 availability. This is in agreement with evidence that Arctic 

 Terns (Sterna paradisaea) showed the earliest and most 

 severe breeding failures at Shetland (Heubeck in Bailey 

 and others 1991). By contrast, some of the larger seabirds 

 with generalist feeding abilities took sand eels when these 

 were abundantly available but switched diet as the sand eel 

 stock declined. 



The relationship between British [Black-legged] 

 Kittiwake breeding success and the Shetland stock of sand 

 eels (Ammodytes) was studied by Harris and Wanless (1990). 

 The evidence that food shortage was responsible for low 

 breeding success was mostly circumstantial but, taken as a 

 whole, compelling. However, the authors concluded that 

 natural factors could have caused the decline in the sand 

 eels, rather than overfishing (Kunzlik in Harris and Wanless 

 1990). They also suggested that herring predation was 

 responsible for the fishery decline. As in the other studies of 

 seabirds and sand lance described above, the authors concluded 

 that more comprehensive studies were needed to allow 

 definitive interpretation of the results. 



More studies on the Pacific sand lance are needed on the 

 west coast of North America, especially on environmental 

 effects and predator influence on survival and abundance. 

 Spawning areas of sand lance need to be identified and 

 managed. The trophic links between sand lance and two 

 other murrelet prey items, euphausiids and herring, indicate 

 a need for comprehensive, long-term study and management. 



Northern Anchovy 



These fish belong to the engraulidae family. They 

 have no adipose fin or lateral line and are closely related 

 to herring. 



The following life history information (for anchovies 

 and sardines) was taken from a draft document (Anonymous 

 1993) which was not completed or published because of a 

 change in Pacific coastal pelagic species management policy 

 between regulatory agencies (Wolf, pers. comm.). 



Northern anchovy are distributed from the Queen 

 Charlotte Islands, British Columbia, to Magdalena Bay, Baja 

 California. The population is divided into northern, central, 

 and southern subpopulations, or stocks. The central 

 subpopulation, which supports significant commercial 

 fisheries in the United States and Mexico, ranges from 

 approximately San Francisco, California, to Punta Baja, Baja 

 California. The northern subpopulation supports a small but 

 locally important bait fishery in Oregon and California. 



Anchovies are small, short-lived fish typically found in 

 schools near the surface. The fish rarely exceed 4 years of age 

 and 18 cm in total length. They have a high natural mortality; 

 approximately 45 to 55 percent of the total stock may die each 

 year of natural causes in the absence of fishing. Northern 

 anchovy eat plankton either directly or by filter feeding. 



Anchovy spawn during every month of the year, but 

 spawning increases in late winter and early spring and peaks 

 from February to April. The eggs, found near the surface, are 

 typically ovoid and translucent and require two to four days 

 to hatch, depending on water temperature. Anchovy are all 

 sexually mature at age 2. The fraction of one-year-olds that 

 is sexually mature in a given year depends on water 

 temperature and has been observed to range from 47 to 100 

 percent (Methot in Anonymous 1993). 



Northern anchovy in the central subpopulation are 

 harvested by commercial fisheries in California and Mexico 

 for reduction, human consumption, live bait, dead bait, and 

 other nonreduction commercial uses. Anchovy landed in 

 Mexico are used primarily for reduction although small 

 amounts are probably used as bait. Small quantities of the 

 northern subpopulation are taken off Oregon and Washington 

 for use as dead bait. 



Anchovy landed by the reduction fisheries are converted 

 to meal, oil, and soluble protein products sold mainly as 

 protein supplements for poultry food and also as feed for 

 pigs, farmed fish, fur-producing animals, laboratory animals, 

 and household pets. Meal obtained from anchovy is about 65 

 percent protein. 



Anderson and others (1980) compared estimates of 

 anchovy biomass and catch statistics to Brown Pelican 

 (Pelecanus occidentalis californicus) reproductive success. 

 Brown Pelican diet was composed of 92 percent anchovies 

 in the Southern California Bight (SCB) study area. Mean 

 SCB anchovy biomass (square miles of anchovy schools) 

 and mean pelican reproductive rate (number of fledglings 

 per nesting attempt) were highly correlated. It was estimated 

 that a minimum anchovy biomass of 43 square miles was 

 necessary for maintaining the existing pelican reproductive 

 rate, though it was recognized that the rate would have to 

 increase in order to at least maintain the pelicans in the SCB. 

 Secondly, the minimum biomass estimate was almost twice 

 the forage reserve which was recommended at the time in 

 the Anchovy Management Plan. They regarded the 

 information as preliminary and concluded that better estimates 

 of the forage reserve were needed. 



A similar relationship between anchovies and Elegant 

 Terns (Sterna elegans) was described by Schaffner (1986). 

 Breeding pairs of Elegant Terns and estimates of anchovy 

 spawning biomass were significantly correlated for the period 

 of 1979 through 1983. Additionally, extensive overlap in age 

 compositions of the tern and fishery samples suggested they 

 were using similar resources and the potential for competition 

 existed. Anchovies constituted more than 86 percent of the 

 chick regurgitations when population size peaked. Schaffner 

 (1986) pointed out the similarities to the Brown Pelican 



236 



USDA Forest Service Gen. Tech. Rep. PSW-152. 1995. 



