energy from ingestion in a suboptimal lattice 

 than that required to swim between the nodes 

 is not possible. While it is obvious that a fish 

 can remain in a suboptimal or unsuitable lat- 

 tice for a relatively short period of time, a fish 

 can remain in an optimal lattice indefinitely. 



Let us now set our fish forage lattice system 

 in motion. First, we consider only space-time 

 points that are contained in a region where the 

 physical environment is tolerable for the spe- 

 cies of interest. Next, we find a set of space- 

 time points that contains suitable and most 

 likely optimal lattices for both spawning parents 

 and progeny. Now we reiterate that the space- 

 time points are simply fixtures in space but the 

 quality of a forage lattice depends upon the 

 physiology, behavior, and density of the forages 

 of interest. Migration becomes necessary when 

 fish are forced to venture from space points 

 that are optimal. "Leaving" optimal space 

 points probably occurs in two general ways. In 

 the first, the forage structure at a space point 

 remains essentially constant over time, but as 

 a fish grows the forage lattice at the space 

 point becomes nonoptimal owing to size- or 

 age-specific food habits on the part of the for- 

 ager. In the second, a space-time point that 

 has an optimal lattice has its lattice modified 

 owing to seasonal changes, intraspecific com- 

 petition, or even the predatory effects of the 

 forager upon the forage. 



Thus, the causal mechanism for movements 

 and migrations would appear to involve, rather 

 intimately, the temporal-spatial distribution of 

 suitable energy as well as the energetic de- 

 mands of the forager--both in terms of the 

 quantity of energy and the quality of energy 

 (i.e., the animal must be able to catch and in- 

 gest the "energy"). As some relatively seden- 

 tary fish evolved and developed specializations, 

 their forage requirements and available forage 

 became modified. In order to obtain sufficient 

 energy resources the fish needed to evolve a 

 behavior where they could continually optimize 

 the forage lattice. The result of the sequential 

 optimization procedure is migration, which as 

 we have shown in this paper, is highly developed 

 in the albacore of the North Pacific Ocean. 



Possible Genetic Effects of Fishing 



Another question of interest in considering 

 large fishery-related declines in the abundance 

 of fish stocks--such as those that might be 

 implied by the decline in apparent abundance of 

 the albacore--concerns the effects of fishing 



on the genetic structure of the fish populations. 

 Modification of the genetic structure of a popu- 

 lation could result from fishing through some 

 form of genetic selection. 



Before we consider genetic selection per se, 

 let us consider selection in general. We define 

 selection in the context of a sampling proce- 

 dure. If sampling is random, then selection 

 does not operate. If the sampling procedure is 

 not random then selection operates. In nonran- 

 dom sampling those elements in the population 

 that have a relatively high probability of being 

 included in the sample are positively selected 

 and those that have a low probability of being 

 included in the sample are negatively selected. 



Selection must operate with respect to some 

 attribute or set of attributes of the individuals 

 that are to be sampled. A s an example, the 

 examination of a sample of fish by a biologist 

 might be considered as a multistage sampling 

 process in which the selection attribute is the 

 length of the fish. Thus, nature might take a 

 nonrandom sample from the population and 

 place it on the fishing grounds; then the fishing 

 gear might select a nonrandom sample of the 

 fish on the fishing grounds; and then the biolo- 

 gist samples the fish that are caught (it is in- 

 teresting to note that in many fisheries it is 

 practically impossible for a biologist to take a 

 truly random sample of fish). 



If the attribute or set of attributes involved 

 in the fishing-selection process is genetically 

 controlled, then it is implicit that fishing will 

 remove certain phenotypes from the population 

 at the expense of those genotypes that are 

 either unselected or negatively selected. Sup- 

 pose, as we have postulated, that a fish's exis- 

 tence at a particular space-time point is the 

 result of some genotypic expression. Thus, in 

 the albacore, we would postulate that its migra- 

 tion pattern is the result of some genetic ex- 

 pression. Basically, the albacore fishing oper- 

 ates at three stations along the migratory path 

 of the albacore. The majority of the albacore 

 appear to migrate through these stations. If 

 the majority of albacore actually do migrate 

 through these stations and the act of migration 

 through the stations is ascribable to a different 

 genetic structure than that which is maintained 

 in individuals that do not migrate through one 

 or more of these stations, then it is clear that 

 a positive genetic selection is being exerted on 

 the individuals that migrate through the sta- 

 tions. Further, it is the genetic constituency of 

 the albacore population which, given a sufficient 



3^ 



