Cohort Dynamics of Summer‐Spawned Bluefish as Determined by Length‐Frequency and Otolith Microstructure Analyses

Abstract

Elucidating recruitment processes in marine fish is difficult when species occupy distinct habitats at different ontogenetic stages and when multiple cohorts determine year‐class strength. Currently, there is insufficient information on the cohort dynamics of the early life history stages of summer‐spawned bluefish Pomatomus saltatrix to critically evaluate each cohort's role in regulating population dynamics. The objective of this study was to provide greater insight into the cohort dynamics of summer‐spawned bluefish during the summer and fall on the inner continental shelf off southern New Jersey. Length‐frequency and otolith microstructure analyses were used to estimate the age, hatch date, and growth of neustonic individuals collected from shelf surface waters during August–October 1998. Bluefish ranged between 9 and 46 d in age, corresponding to back‐calculated hatch dates between 27 June and 13 September. Hatch date frequencies were decomposed into a series of normal curves and identified three cohorts with mean hatch dates occurring in early July (cohort 1), late July to early August (cohort 2), and late August to early September (cohort 3). Cohort‐specific growth rates ranged between 0.28 and 0.81 mm standard length/d. Otolith microstructure analysis revealed that growth was significantly faster for cohort 1 than for the other cohorts, most likely because of spatial and temporal variability in the environment (e.g., temperature) and size‐selective processes (e.g., mortality). Back‐calculated spawning dates indicated that the functional spawning output of bluefish was significantly greater during the first‐quarter phase of the lunar cycle. Collectively, these observations suggest that the cohort structure of bluefish is more complex than previously recognized.

Habitat use, growth, and mortality of post-settlement lane snapper (Lutjanus synagris) on natural banks in the northwestern Gulf of Mexico

“…Cohort-specific differences in growth have been attributed to a variety of factors, including temperature (Taylor and Able, 2006), salinity (Secor et al, 2000), food availability (Cowan and Shaw, 2002;Katersky et al, 2006) and predation mortality (Rilling and Houde, 1999;Taylor and Able, 2006 Habitat-specific variation in growth was observed, with lower rates on the inshore habitat than either the ridge or offshore habitats; however, no significant difference was detected. Differences in growth rates among habitats have been attributed to prey availability (Comyns et al, 2003) and type (Cowan and Shaw, 2002) and assessments of post-settlement growth of red snapper on banks examined in the present study have detected differences in growth among habitats (Rooker et al, 2004;Geary et al, in review).…”

Winter energy storage dynamics and cohort structure of young-of-the-year bluefish Pomatomus saltatrix off North Carolina

“…When this study was initiated, length-frequency distributions of Age-0 bluefish had consistently been described as bimodal, consisting of spring-and summer-spawned bluefish (McBride & Conover 1991, Munch & Conover 2000. However, 3 recent studies have identified at least 3 cohorts of YOY bluefish (Able et al 2003, Wilber et al 2003, Taylor & Able 2006. In the MAB these additional cohorts are likely the result of multiple peaks in summer-spawning activity (Taylor & Able 2006).…”

“…However, 3 recent studies have identified at least 3 cohorts of YOY bluefish (Able et al 2003, Wilber et al 2003, Taylor & Able 2006. In the MAB these additional cohorts are likely the result of multiple peaks in summer-spawning activity (Taylor & Able 2006).…”

“…A majority of YOY bluefish recruiting to the Middle Atlantic Bight (MAB) are thought to originate from either spawning during the spring in the South Atlantic Bight (SAB) with progeny transported north in the Gulf Stream (Kendall & Walford 1979, Hare & Cowen 1996, or summer spawning that occurs on the continental shelf of the MAB (Kendall & Walford 1979, Smith et al 1994. Summer spawning has recently been shown to be complex, consisting of multiple peaks (Taylor & Able 2006) and 2 cohorts of summerspawned fish have been observed in addition to the larger spring-spawned cohort in the MAB (Able et al 2003, Wilber et al 2003.…”

Multiple spawning events promote increased larval dispersal of a predatory fish in a western boundary current

“…Many fish species have complex spawning behaviour, and the timing and location of spawning, in particular, can have a large influence on settlement location and success due to the spatial and seasonal variation in ocean circulation (McEvoy & McEvoy, 1992; Taylor & Able, 2006). Pomatomus saltatrix, for example, is a globally distributed fish (Juanes, Hare, & Miskiewicz, 1996) with recognised spawning migrations in western boundary current systems worldwide (East Australian Current, Gulf Stream, Agulhas Current and Brazil Current).…”