ANDERSON ET AL.: BROWN PELICANS AS ANCHOVY STOCK INDICATORS CalCOFI Rep., Vol. XXI, 1980 BROWN PELICANS AS ANCHOVY STOCK INDICATORS AND THEIR RELATIONSHIPS TO COMMERCIAL FISHING DANIEL W ANDERSON AND FRANKLIN GRESS KENNETH F. MAIS AND PAUL R. KELLY Department of Wildlife and Fisheries Biology California Department of Fish and Game University of California 350 Golden Shore Davis, CA 9561 6 Long Beach, CA 90802 ABSTRACT suggestions based on brown pelican requirements. Seabirds as offshore wildlife resources have largely been unstudied by wildlife managers until recently. Brown RESUMEN pelicans (Pelecanus occidentalis californicus) in South- El estudio de las aves marinas como recursos faunisti- ern California Bight (SCB) have received special at- cos en las zonas lejos de la costa ha sido bastante desa- tention in the past under the Endangered Species Act of tenido hasta fecha reciente por 10s organismos encargados 1973 (ESA). Special consideration is given to species de la fauna silvestre. Los pelicanos gris (Pelecanus oc- with endangered status in commercial fishery manage- cidentalis culifornicus) de la Bahia del Sur de California ment plans mandated by the Fisheries Conservation and han recibido atencion especial con el Endangered Species Management Act of 1976, but such plans also attempt to Act (ESA) de 1973. En 10s planes de administracion de deal positively with all species of seabirds and marine la pesqueria comercial incluidos en el Fisheries Con- wildlife as society’s values change more positively toward servation and Management Act de 1976, se ha prestado such offshore wildlife resources. atencion especial a especies en peligro de desaparicion, Brown pelican breeding status is heavily dependent on per0 esos planes tambien intentan abarcar todas las es- abundance and/or availablility of anchovies during the pecies de aves marinas y de vida marina a medida que prebreeding and breeding periods. This is likely due to the cambian mas 10s valores que la sociedad atribuye a esos dominance of northern anchovy (Engraulis mordax) bie recursos de 10s animales salvajes oceanicos. mass in surface schooling fishery stocks in the SCB. The El pelicano gris depende basicamente de la abundancia predator-prey relationship that involves brown pelicans y/o disponibilidad de anchoveta durante 10s periodos de and anchovies in the SCB is a tenuous one due to 1) the precrianza y crianza. Probablemente esto se debe a que la strong dependence almost solely on anchovies evidenced biomasa de anchoveta del norte (Engraulis mordux) es over the last nine years of study and 2) potential increases dominante en 10s cardumenes de la Bahia del Sur de Cali- of commercial harvest of anchovies since 1979 under fornia. La relacion predador-presa entre el pelicano gris some options of the Anchovy Management Plan pro- y la anchoveta en la Bahia del Sur de California es debil vided by the Pacific Fishery Management Council. There a causa de 1) su casi exclusiva dependencia sobre la an- are also two elements of this interaction that complicate choveta, segun se evidencia en 10s ultimos nueve aiios de straightforward management of pelicans: a) implementa- estudio, y 2) incrementos en la captura comercial de an- tion of a liberal harvest option under the Anchovy Man- chovetas desde 1979 bajo algunas opciones del Anchovy agement Plan rather than a more conservative one and b) Management Plan segun las provisiones del Pacific Fish- increasing anchovy harvests in Mexico. Unless anchovies ery Management Council. En esta interaccion hay tambien are replaced by another prey, breeding pelicans may dos elementos que complican la administracion directa ultimately require a larger forage reserve of anchovies, de pelicanos: a) la implantacion de una opcion de pesca offshore refuges (critical habitat under the ESA), and amplia bajo el plan de administracion de la pesqueria de possibly more conservative quotas in the anchovy reduc- anchovetas, en lugar de una mas conservadora, y b) el tion fishery. A management plan for brown pelicans and incremento de pesca de anchoveta en Mexico. A menos other seabirds in the SCB has not yet been developed by que se reemplacen las anchovetas con otra presa, 10s peli- the appropriate agencies. canos en estado de crianza podrian requerir una reserva Past anchovy harvests (pre-1979) probably did not mas grande de aliment0 de anchovetas, refugios fuera de detectably disrupt the pelican/anchovy relationship, al- la costa (habitat critic0 bajo el ESA), y posiblemente though at the higher observed levels of pelican reproduc- cuotas mas conservadoras reduciendo la pesqueria de tion (coincident with higher levels of anchovy biomass anchoveta. Las agencias responsables no han desarrollado and catch), pelican reproductive rate was not maximal. todavia un plan para la conservacion de 10s pelicanos gris This is more likely because pollution may still be chroni- y otras aves de la Bahia del Sur de California. cally affecting pelican reproduction. Anchovy harvests La pesqueria de anchoveta anterior a 1979 probable- under an optimum yield scheme will be monitored closely mente no afecto notablemente la relacion pelicano/ancho- for possible effects on pelican reproduction. Although veta, aunque se ha observado que a niveles elevados de more detailed studies are needed, we provide some initial reproduccion del pelicano (que coinciden con niveles mas 54 ANDERSON ET AL.: BROWN PELICANS AS ANCHOVY STOCK INDICATORS CalCOFI Rep., Vol. XXI, 1980 elevados de captura y biomasa de anchoveta), el indice see Radovich 1979, Radovich and MacCall 1979, reproductor del pelicano no alcanzo un maximo. Proba- MacCalll980 for further details and discussion) that will blemente se debe a que la contaminacionpuede estar ah ideally insure that northern anchovies (Engraulis mordax) afectando cronicamente la reproduccion del pelicano. La will not be overfished. Several potential problems exist, pesca de anchoveta bajo un esquema de rendimiento op- however, off southern California that might affect an- timo sera cuidadosamenteinspeccionada para determinar chovy predators, in this case namely the brown pelican: posibles efectos sobre la reproduccion del pelicano. Aunque 1) increasing Mexican harvests of anchovies (Chavez et se necesitan estudios mas detallados, proveemos algunas al. 1977) and 2) increased harvests off southern Cali- sugerencias iniciales basadas en 10s requisitos del peli- fornia under a liberal option provided in the Anchovy can0 gris. Management plan (PFMC 1978; McCall 1980). Values of offshore wildlife and the needs of those re- INTRODUCTION sources further complicate a management situation in the As wildlife values change in our society, the chances SCB that May et al. (1979) have summarized as such: for socioeconomic confiict increase. This will be espec- “This is a particularly clear example of a complex sit- ially true where commercially harvested resources might uation where biology, economics, and politics roil to- relate in some way to asthetic or noncommerial ones, gether, and it is doubtful whether any ‘scientific’ prin- especially through conflicts in different value systems ciples of management are particularly relevant.” We are (see Langford and Cocheba 1978; Bart et al. 1979; and not so sure that the situation here is as hopeless as might others). In the past, seabirds and other marine wildlife be implied; and in fact, we believe that the potential for were viewed as undesirable competitors. Marine birds, a interdisciplinary and interagency collaboration in the “neglected” resource in North America until recently SCB area is great. Here we intend to approach this situa- (Bartonek and Sow1 1974), are often dependent on com- tion from the viewpoint of one local population of sea- mercially utilized resources, and only recently are they bird: brown pelicans nesting on islands off southern being viewed by wildlife managers as valuable, conserv- California. able, and manageable resources in themselves (see Cline et al. 1979; Nisbet 1979; and this symposium). The al- PELICAN DEPENDENCE ON AND ternative approach of using seabird population para- RELATIONSHIPS TO ANCHOVIES meters as indices to aid the monitoring of commercially Keeping in mind that we are here refemng to breeding valuable fishery stocks is a technique with much pc~ populations and productivity of SCB brown pelicans only tential in providing added, independent input for fishery (not migrants), previous research (Anderson et al. in pre- managers. paration, Gress et al. in preparation) has established that: Some seabirds such as the California brown pelican 1) There are only two major brown pelican nesting (Pelecanus occidentalis calfornicus), and its habitat, are colonies in the SCB, Anacapa Island (and associated given special protection under the Endangered Species Scorpion Rock) and Isla Coronado Norte just across Act of 1973 (ESA); this act enables the various manage- the Mexican border. On occasion, pelicans have also ment agencies to cooperate on the management of off- nested on such islands as Santa Barbara, Prince, and shore ecosystems. others (Gress 1970). The collapse of the anchoveta (Engruulis ringens) 2) Pelican breeding effort at both colonies (numbers fishery in Peru (Clark 1977) and associated detrimental of pairs that attempt to breed each year) is probably effects on seabirds, both before the collapse (intentional dependent largely on regional levels of anchovy and predicted population reductions of seabirds due to abundance, but this relationship is difficult to docu-