Predicting Crappie Recruitment in Ohio Reservoirs with Spawning Stock Size, Larval Density, and Chlorophyll Concentrations

Abstract

Abstract.-Stock-recruit models typically use only spawning stock size as a predictor of recruitment to a fishery. In this paper, however, we used spawning stock size as well as larval density and key environmental variables to predict recruitment of white crappies Pomoxis annularis and black crappies P. nigromaculatus, a genus notorious for variable recruitment. We sampled adults and recruits from 11 Ohio reservoirs and larvae from 9 reservoirs during 1998-2001. We sampled chlorophyll as an index of reservoir productivity and obtained daily estimates of water elevation to determine the impact of hydrology on recruitment. Akaike's information criterion (AIC) revealed that Ricker and Beverton-Holt stock-recruit models that included chlorophyll best explained the variation in larval density and age-2 recruits. Specifically, spawning stock catch per effort (CPE) and chlorophyll explained 63-64% of the variation in larval density. In turn, larval density and chlorophyll explained 43-49% of the variation in age-2 recruit CPE. Finally, spawning stock CPE and chlorophyll were the best predictors of recruit CPE (i.e., 74-86%). Although larval density and recruitment increased with chlorophyll, neither was related to seasonal water elevation. Also, the AIC generally did not distinguish between Ricker and Beverton-Holt models. From these relationships, we concluded that crappie recruitment can be limited by spawning stock CPE and larval production when spawning stock sizes are low (i.e., CPE , 5 crappies/net-night). At higher levels of spawning stock sizes, spawning stock CPE and recruitment were less clearly related. To predict recruitment in Ohio reservoirs, managers should assess spawning stock CPE with trap nets and estimate chlorophyll concentrations. To increase crappie recruitment in reservoirs where recruitment is consistently poor, managers should use regulations to increase spawning stock size, which, in turn, should increase larval production and recruits to the fishery.

Standard Assessments Reveal Context‐Dependent Responses of Crappie Populations to a Length‐Based Regulation in Ohio Reservoirs

“…Further, declines in growth caused by increased intraspecific competition may lead to decreased reproductive investment and reductions in recruitment (Bunnell et al. ; Michaletz ). Concentrating harvest on large individuals has been shown to cause recruitment overfishing in salmonids by removing the individuals that contribute the greatest reproductive output (Sánchez‐Hernández et al.…”

Decline in bloater fecundity in Southern Lake Michigan after decline of Diporeia

“…Hence, we use the Emery and Brown (1978) regression [Fecundity = −580.6 + 58.88(weight); note Emery and Brown (1978) failed to include the negative sign in front of the intercept] for the 1963-1984 year-classes, and our regression for 1985-2004 year-classes. To fit the Ricker (R =Se [a-bS] e ɛ ) and BevertonHolt (R ={aS /[b + S]}e ɛ ) models, where R equals age-3 bloater recruits (in millions of individuals), S equals population egg production (in billions of eggs), and e ɛ equals the lognormal error term, we followed Bunnell et al (2006b) where both sides of the equation were log etransformed [Ricker: log e (R) = log e (S)+ a − bS + ɛ, Beverton and Holt: log e (R) = log e (aS) − log e (b + S)+ɛ)] and non-linear regression (Proc NLIN, SAS Institute, 1999) was used to estimate the parameters. For each model, r 2 was calculated as the model sum of squares divided by the corrected total sum of squares.…”

Dynamic angling effort influences the value of minimum‐length limits to prevent recruitment overfishing

“…Similarly, angling exploitation likely caused recruitment overfishing of a Kansas walleye population (Quist et al 2010). A recreational black crappie, Pomoxis nigromaculatus (LeSueur), fishery exerted a 42% exploitation rate, which was near the recruitment overfishing threshold (Dotson et al 2009). Bunnell et al (2006 suggested that harvest restrictions would improve recruitment of white crappie P. annularis for some Ohio reservoirs, which indicated that some stocks were recruitment overfished.…”