Density-dependent habitat use and growth of an estuarine fish

Abstract

Density dependence can stabilize or destabilize population size through negative or positive feedback controls operating over different spatial and temporal scales. While many species have been shown to exhibit density dependence, the topic has received little attention in estuaries where environmental variability and larval supply are often considered to be the primary drivers of population dynamics. We used multiple long-term, fishery-independent data sets and a unique modeling approach to test the hypothesis that juvenile red drum (Sciaenops ocellatus) exhibit density-dependent habitat use and growth rates in estuaries in North Carolina, USA. Age-1 red drum exhibited density-dependent habitat use after accounting for environmental and landscape variables, disproportionately increasing northward and coastward in the study area at high abundance. Apparent individual growth rates of age-0 and age-1 red drum were generally negatively related to the abundance of their own age classes, but evidence of density-dependent growth rates for age-2 red drum was weak to nonexistent. Changes in spatial distribution of red drum when overall abundance was high did not overcome density-dependent effects on individual growth rates. Thus, density-dependent effects have potential negative feedbacks on population growth in estuaries and should not be ignored in future theoretical or empirical estuarine studies.Résumé : La dépendance de la densité peut stabiliser ou déstabiliser la taille d'une population par l'entremise de rétroac-tions négatives ou positives oeuvrant à différentes échelles spatiales et temporelles. S'il a été démontré que de nombreuses espèces présentent une dépendance de la densité, le sujet a reçu peu d'attention en ce qui concerne les estuaires, où la variabilité environnementale et l'abondance des larves sont souvent considérées comme les principaux moteurs de la dynamique des populations. Nous avons utilisé de multiples ensembles de données à long terme indépendants de la pêcherie et une nouvelle approche de modélisation pour tester l'hypothèse selon laquelle l'utilisation de l'habitat et les taux de croissance des tambours ocellés (Sciaenops ocellatus) juvéniles dans les estuaires de la Caroline du Nord (États-Unis) sont dépendants de la densité. À forte abondance, l'utilisation de l'habitat des tambours ocellés d'un an était dépendante de la densité si les variables environnementales et du paysage étaient prises en compte, cette dépendance augmentant disproportionnellement vers le nord et les côtes dans la zone d'étude. Les taux de croissance individuels apparents pour les tambours ocellés de zéro et un an présentaient généralement une relation négative avec l'abondance de la classe d'âge concernée, mais les données reflétant des taux de croissance dépendants de la densité pour les tambours ocellés de deux ans étaient rares à non existantes. Des modifications de la répartition géographique des tambours ocellés durant les périodes de grande abondance générale ne compensaient pas les effets dépendants de la d...

Environmental change drives long-term recruitment and growth variation in an estuarine fish

“…Furthermore, there are likely to be feedbacks between recruitment and growth operating at some scale that whist not detected here could also affect population productivity (e.g. maternal size and reproductive output Walsh et al ., ; or density‐dependence Bacheler et al ., ). Similar uncertainty will surround future productivity estimates of other estuarine fishes that respond to multiple environmental drivers and can only be resolved with more sophisticated stock assessment techniques based on comprehensive empirical data sets such as those presented here.…”

“…Carry‐over effects from variable environmental conditions experienced as a juvenile (e.g. inter‐annual variation in larval food availability) can manifest throughout an individual's life in terms their of growth (Whitten et al ., ), and year class strength can also have persistent effects on growth through density‐dependent competition for resources among same‐aged individuals (Amundsen et al ., ; Bacheler et al ., ). Our results suggest that persistent year class growth differences are primarily due to abiotic rather than density dependence effects as we failed to detect a relationship between growth and year class strength ( sensu Lobón‐Cerviá, ).…”

Fishing constrains phenotypic responses of marine fish to climate variability

“…The release from density dependence is therefore not confined only to fish within the same cohort (e.g. Bacheler, Buckel, & Paramore, ; Whitten, Klaer, Tuck, & Day, ), but instead manifests across all age and size classes.…”

Marked deleterious changes in the condition, growth and maturity schedules of Acanthopagrus butcheri (Sparidae) in an estuary reflect environmental degradation

“…It is thus noteworthy that density dependent factors were also considered responsible for the decline in growth of Micropogonias undalatus in the Neuse River Estuary (Eby et al, 2005). In addition, the use of fishery-independent data demonstrated that the growth of the 0þ and 1þ age classes of the red drum Sciaenops ocellatus were negatively related to the density of their own age classes (Bacheler et al, 2012). Furthermore, analysis of long-term records of size at age and biomass data for 16 fish populations revealed that the growth of individuals in nine of those populations was inversely related to density (Lorenzen and Enberg, 2002).…”