Estimating live standard length of net-caught walleye pollock (Theragrachalcogramma) larvae using measurements in addition to standard length

摘要

Accurate measurement of larval fish lengths from ichthyoplankton samples is critical in the estimation of growth, birthdate and mortality. It is well known that larvae shrink in length 1) when caught in plankton nets (Theilacker, 1980; Hay, 1981), 2) between the time of collection and preservation, and 3) afterwards from the effects of preservation in chemicals or from freezing (Theilacker, 1980; Fowler and Smith, 1983; Yin and Blaxter, 1986). Shrinkage caused by the plankton net (the net can damage a larva's integument; Holliday and Blaxter, 1960) and by delays in preservation can be up to 40 percent of the initial live length (Hay, 1981). In some cases, measurements of larval body length may be unsuitable for growth estimation (Jennings, 1991). In other cases, algorithms have been developed to estimate live lengths from preserved larvae (Bailey 1982, Hjorleifsson and Klein-MacPhee, 1992; Fey, 1999) and from net-caught and preserved larvae (Theilacker, 1980; Theilacker and Porter, 1995; Fox, 1996). It has also been noted that constant shrinkage-correction factors should be applied cautiously (Pepin et al., 1998).