Abstract:The ecology of overwintering young-of-the-year bluefish Pomatomus saltatrix off North Carolina, USA, was examined for the 2001 and 2002 year-classes, to test the hypothesis that overwinter mortality affects the recruitment of summer-spawned bluefish. A trawling survey was conducted in Onslow Bay, North Carolina, from October 2001 to May 2002 and from September 2002 to June 2003 to determine bluefish abundance, cohort structure, energy density of white muscle and liver, and gut fullness. Up to 4 transects rangi… Show more
“…On 19 November 2001, tanks were stocked with 15 SP or SU bluefish (n = 3 replicate tanks per treatment combination). Cohort assignment was based on bimodal length/frequency distributions of YOY bluefish collected in NC during fall 2001 (Morley et al 2007). Mean (± SD) initial fork lengths (FL) of SP and SU bluefish were 264 ± 16.6 mm and 206 ± 12.0 mm, respectively (Student's t-test, p < 0.01).…”
Section: Methodsmentioning
confidence: 99%
“…Wild bluefish for this analysis were trawled from continental shelf (5 to 20 m depth) habitats in Onslow Bay, North Carolina, during February and May 2002 (Morley et al 2007). Condition indices included liver dry mass, liver lipid and ash content, WM lipid density, WM ash content and total wet body mass.…”
Section: Methodsmentioning
confidence: 99%
“…While cold (<15°C) temperatures occurred for bluefish subjects during January and February, it is surprising that lipid reserves remained virtually depleted in late May. Water temperatures in the mesocosm tanks during April and May (>15°C) were within preferred ranges of bluefish and presumably suitable for feeding and energy storage (Lund & Maltezos 1970, Morley et al 2007. It is noteworthy that similar temperatures experienced by bluefish subjects during the previous fall were associated with rapid lipid storage by both cohorts.…”
Section: Lipid Storage Patterns: Spring Vs Summer Cohortmentioning
confidence: 98%
“…This phenomenon would give the impression of the summer cohort's disappearance despite their presence in the adult population. Laboratory and field observations of juvenile bluefish growth do not support this explanation (McBride et al 1993, Buckel et al 1998, Morley et al 2007). Third, the summer cohort may recruit to localities outside the MAB, i.e.…”
Bluefish Pomatomus saltatrix have experienced declines in recruitment and adult abundance along the US East Coast since the mid-1980s. At the onset of winter, young-of-the-year (YOY) bluefish exhibit a multimodal size distribution including larger, spring-spawned fish (spring cohort) and smaller, summer-spawned fish (summer cohort). Declines in the adult stock appear to coincide with declines in recruitment success of the summer cohort. We investigated the hypothesis that poor recruitment success of the summer cohort results from size-selective winter mortality. Winter mesocosm experiments were conducted to examine the effects of cohort of origin (spring vs. summer) and food availability (fed vs. unfed) on winter survival of YOY bluefish. Spring fish entered winter with significantly greater lipid reserves than summer fish. When fed, both cohorts stored lipids during late fall, depleted lipid reserves during winter, and experienced high overwinter survival. When starved, both cohorts mobilized lipids from multiple depots (liver, viscera, white muscle, red muscle, skin) and summer fish experienced starvation mortality ~6 wk prior to spring fish. Although summer fish were more susceptible to winter starvation than spring fish, their starvation endurance (> 90% survival probability after 120 d) appeared more than adequate to survive natural winter conditions. Interestingly, spring fish suffered a brief mortality event during January when water temperatures dropped briefly below 6°C, suggesting that larger individuals are less tolerant of acute cold stress. The remarkable starvation endurance of summer-spawned bluefish, coupled with their capacity for rapid lipid storage during fall and reduced rates of lipid depletion at low temperatures, implies that members of this cohort are physiologically well-equipped to survive their first winter of life. Our findings are inconsistent with the hypothesis that winter starvation accounts for decreased recruitment of the summer cohort to the western Atlantic stock.
“…On 19 November 2001, tanks were stocked with 15 SP or SU bluefish (n = 3 replicate tanks per treatment combination). Cohort assignment was based on bimodal length/frequency distributions of YOY bluefish collected in NC during fall 2001 (Morley et al 2007). Mean (± SD) initial fork lengths (FL) of SP and SU bluefish were 264 ± 16.6 mm and 206 ± 12.0 mm, respectively (Student's t-test, p < 0.01).…”
Section: Methodsmentioning
confidence: 99%
“…Wild bluefish for this analysis were trawled from continental shelf (5 to 20 m depth) habitats in Onslow Bay, North Carolina, during February and May 2002 (Morley et al 2007). Condition indices included liver dry mass, liver lipid and ash content, WM lipid density, WM ash content and total wet body mass.…”
Section: Methodsmentioning
confidence: 99%
“…While cold (<15°C) temperatures occurred for bluefish subjects during January and February, it is surprising that lipid reserves remained virtually depleted in late May. Water temperatures in the mesocosm tanks during April and May (>15°C) were within preferred ranges of bluefish and presumably suitable for feeding and energy storage (Lund & Maltezos 1970, Morley et al 2007. It is noteworthy that similar temperatures experienced by bluefish subjects during the previous fall were associated with rapid lipid storage by both cohorts.…”
Section: Lipid Storage Patterns: Spring Vs Summer Cohortmentioning
confidence: 98%
“…This phenomenon would give the impression of the summer cohort's disappearance despite their presence in the adult population. Laboratory and field observations of juvenile bluefish growth do not support this explanation (McBride et al 1993, Buckel et al 1998, Morley et al 2007). Third, the summer cohort may recruit to localities outside the MAB, i.e.…”
Bluefish Pomatomus saltatrix have experienced declines in recruitment and adult abundance along the US East Coast since the mid-1980s. At the onset of winter, young-of-the-year (YOY) bluefish exhibit a multimodal size distribution including larger, spring-spawned fish (spring cohort) and smaller, summer-spawned fish (summer cohort). Declines in the adult stock appear to coincide with declines in recruitment success of the summer cohort. We investigated the hypothesis that poor recruitment success of the summer cohort results from size-selective winter mortality. Winter mesocosm experiments were conducted to examine the effects of cohort of origin (spring vs. summer) and food availability (fed vs. unfed) on winter survival of YOY bluefish. Spring fish entered winter with significantly greater lipid reserves than summer fish. When fed, both cohorts stored lipids during late fall, depleted lipid reserves during winter, and experienced high overwinter survival. When starved, both cohorts mobilized lipids from multiple depots (liver, viscera, white muscle, red muscle, skin) and summer fish experienced starvation mortality ~6 wk prior to spring fish. Although summer fish were more susceptible to winter starvation than spring fish, their starvation endurance (> 90% survival probability after 120 d) appeared more than adequate to survive natural winter conditions. Interestingly, spring fish suffered a brief mortality event during January when water temperatures dropped briefly below 6°C, suggesting that larger individuals are less tolerant of acute cold stress. The remarkable starvation endurance of summer-spawned bluefish, coupled with their capacity for rapid lipid storage during fall and reduced rates of lipid depletion at low temperatures, implies that members of this cohort are physiologically well-equipped to survive their first winter of life. Our findings are inconsistent with the hypothesis that winter starvation accounts for decreased recruitment of the summer cohort to the western Atlantic stock.
“…Also, due to the lack of previously published studies that report summer lipid values for age-0 bluefish, we were unable to compare the cohort-specific C:N lipid proxy patterns that we observed to values from the same month(s) from other regions or years. Still, it is worth noting recent work by Slater et al (2007) and Morley et al (2007) that found that spring and summer cohorts of age-0 bluefish manifested different energy allocation strategies by fall; members of the spring-spawned cohort entered the October-November overwintering period with higher lipid reserves than summerspawned fish that presumably shunted more energy into somatic growth. We observed the opposite pattern, i.e.…”
In coastal regions, age-0 juveniles of many fish species are capable of recruiting to either marine or estuarine nursery habitats, yet the ecological consequences for cohorts that use marine versus estuarine nurseries is poorly understood. In the present study, stable isotope (δ 13 C, δ 15 N) and stomach contents data were used to compare trophic ecology associated with differential habitat use for age-0 bluefish Pomatomus saltatrix and bay anchovy Anchoa mitchilli from 2 habitats: Maryland's (USA) inner continental shelf (shelf) and lower Chesapeake Bay (estuary). Bluefish occupied equivalent trophic positions (approx. 4.0 to 4.2; δ 15 N-and diet-based estimates) as tertiary consumers in the shelf and estuary. In contrast, bay anchovy were secondary-tertiary consumers with trophic position estimates of 3.5 to 3.8 in the shelf and 3.5 in the estuary. A C:N ratio proxy for lipid content was higher in the shelf cohorts for both species, and weight-at-length was also higher for shelf bay anchovy than estuarine bay anchovy. Estuarine cohorts of both species occupied a larger isotopic niche (i.e. convex hull area), yet 2-source mixing model results indicated that estuarine cohorts derived > 80% of their biomass from pelagic food webs alone. Conversely, shelf cohorts more equitably integrated pelagic (bluefish: 45 ± 7% [SD], bay anchovy: 46 ± 12%) and benthic food webs. The present study indicates that the juvenile trophic niche of these species can vary significantly across habitats and provides initial evidence that cohorts recruiting to Maryland's shelf can realize more diverse (i.e. utilization of multiple food webs) or superior (i.e. increased condition -bay anchovy only) foraging conditions than cohorts recruiting to proximal estuaries.
Large-scale habitat preferences of riverine taxa are not always revealed by examining community data. Here, we show how lipid and growth can be used to evaluate hydrologic habitat preferences of fishes resilient to river fragmentation (i.e. species that can tolerate river fragmentation by dams, but not collapse). Lipid content was examined for seven fishes in a major southeastern USA reservoir and its largest lotic tributary over the 5 years. Controlling for effects of sex, size and year of collection, largemouth bass, spotted bass and black crappie had significantly higher lipid in lentic habitat. Conversely, channel catfish and freshwater drum had significantly higher lipid in lotic habitat. There were no significant differences in lipid of bluegill and blacktail shiner between hydrologic habitat types. Fish growth produced concordant results as largemouth bass and spotted bass had significantly faster growth in lentic habitat, whereas channel catfish and freshwater drum had significantly faster growth in lotic habitat. We were also able to document a synchronous spike in lipids of these species in both habitat types during a major drought. We surmise that the spike was driven by enhanced primary production, predator-prey concentration and possibly also reduced reproduction during intense drought. Two conclusions are drawn from this study as a whole. First, long-term lipid and growth observations hold promise for evaluating ecological effects of droughts over long time spans. Second, population characteristics are excellent indicators of habitat preferences and could be used more broadly to elucidate how organisms react to river ecosystem fragmentation and restoration initiatives.
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