Spatiotemporal trends and drivers of fish condition in Chesapeake Bay

Abstract

Measures of condition in fishes are often used to assess the general well-being of fish populations since condition reflects the biotic and abiotic factors experienced by individuals over moderate time scales. Fish condition can also be used as an indicator of ecosystem suitability in the context of ecosystembased management. From an ecosystem perspective, evaluation of fish condition is best described over multiple spatiotemporal scales and in a multi-species context. This study analyzed 14 yr (2002−2015) of fisheries-independent trawl survey data to evaluate trends in condition for 16 demersal fishes inhabiting Chesapeake Bay, the largest estuary in the USA. Seasonal and spatial variability in condition were inferred from linear mixed-effects models, while dynamic factor analysis (DFA) was used to reveal coherence among and drivers of annual trends in condition across all species and for 3 subgroups representing trophic guilds. Patterns of intra-annual condition varied among species, likely reflecting life history strategies and physiological responses to seasonal environmental conditions, while spatial patterns showed improved condition for both coastal and oligohaline species with increasing distance from their source. Annual trends in condition showed remarkable coherence for all fishes and for species within each trophic guild, suggesting that factors influencing condition-based indicators of ecosystem suitability operate at the community level. Spring mean surface chl a concentration was included in the selected DFA model for nearly all groups (exception: benthivores) and was statistically significant for several species, indicating the importance of bottom-up processes on bay-wide annual fish condition.KEY WORDS: Fish condition · Bottom-up controls · Chesapeake Bay · Ecosystem-based management · Linear mixed effects models · LME · Dynamic factor analysis · DFA Chesapeake Bay fishes exhibited coherence to a common trend of annual condition. Correlations between condition and chl a suggest bottom-up forcing.

Lead in piscivorous raptors during breeding season in the Chesapeake Bay region of Maryland and Virginia, USA

“…In higher salinity waters, osprey eat almost no catfish but instead forage on a greater proportion of filter‐feeding anadromous and saltwater fish. Gizzard shad are detritivores, lower on the food chain than catfish and therefore less likely to accumulate trace metals (Latour et al ). It is therefore not surprising that only one of the gizzard shad we sampled had lead concentrations above the LOD (Table ).…”

“…In contrast, the majority of the nestling osprey we tested on the Eastern Shore nested in high-salinity environments. Gizzard shad are detritivores, lower on the food chain than catfish and therefore less likely to accumulate trace metals (Latour et al 2017). Likewise, there is a demonstrated dietary response by osprey in relation to salinity in the Chesapeake Bay region (Glass and Watts 2009).…”

Nursery Habitat Quality Assessed by the Condition of Juvenile Fishes: Not All Estuarine Areas Are Equal

“…Upestuary habitats in the James, York, and Rappahannock subestuaries may provide higher quality habitats for coastal species like juvenile Atlantic croaker and summer flounder than previously expected. Improved condition of coastal species in upestuary habitats has been observed for a suite of trophic guilds and life stages (Latour et al 2017). Juveniles in upestuary habitats may be exposed to energy-rich prey resources that are less available in downestuary regions, or reduced predation pressure in upestuary regions may allow for more frequent feeding activity.…”

Food limitation of juvenile marine fish in a coastal and estuarine nursery

“…For example, observed growth rates often remain nearly optimal, even when food is limiting, because slow-growing individuals have lower survival and are thus rarely sampled (Le Pape and Bonhommeau 2015). Another approach is to correlate time-series of food supply and fish abundance, fish condition or survival (Beaugrand et al 2003;Okamoto et al 2012;Latour et al 2017), but long-term datasets with both prey and predator indices are rarely available. Alternatively, the extent to which food is limiting can be inferred directly from the proportion of prey production that is consumed by their predators (Evans 1983;Boisclair and Leggett 1985;Collie 1987;Vinagre and Cabral 2008).…”