Differences In Timing Of Spawning Research Articles

Influence of behavior and mating success on brood-specific contribution to fish recruitment in ponds

One source of uncertainty in predicting the response of populations to exploitation is individual differences within a population in both vulnerability to capture and contribution to population renewal. For species with parental care, individuals engaged in nesting behavior are often targeted for exploitation, but predicting outcomes of this nonrandom vulnerability will depend in part on an understanding of how parental traits are related to potential for brood contribution to the population. Variation in brood-specific contribution to recruitment of largemouth bass (Micropterus salmoides), a fish species with extended parental care, was quantified to determine if differences in mating success, parental care behaviors, and timing of reproduction influenced offspring recruitment. Dependence of these relationships on brood predation was tested in communities that differed in the presence of bluegill, Lepomis macrochirus, an important nest predator. Daily snorkel surveys were conducted in experimental ponds during spring to monitor male spawning and parental care behaviors in populations of largemouth bass. Tissue samples collected from larvae in nests were used to develop brood-specific DNA fingerprints for determining nest origins of fall recruits. Largemouth bass spawning period in bluegill ponds was longer and more variable in duration, with lower, more variable mating success, than in ponds without bluegill. In all populations, only one or two broods provided the majority of recruits, and these were broods produced during the earliest days of spawning by the oldest, largest males. In bluegill ponds, brood contribution from earliest nests also increased with brood size. Earliest nesters were the oldest males, and recruits from these nests were often above average in body size. Offspring needed to be guarded to at least swim-up larval stage to contribute any recruits. Termination of parental protection before offspring were free swimming mainly occurred with broods guarded by smaller males in ponds with brood predators. These age- and size-specific differences in timing of spawning and duration of parental care are consistent with influences of residual reproductive value and energetic constraints on reproductive behavior. Furthermore, these patterns of individual contribution to recruitment imply that fisheries that selectively target either nesting individuals or larger, older males could potentially decrease recruitment at the population scale.

Use of Microsatellites to Determine Population Structure and Migration of Pacific Herring in British Columbia and Adjacent Regions

AbstractThis study assessed genetic population structure of Pacific herring Clupea pallasii in British Columbia and adjacent regions by analyzing microsatellite variation; the utility of microsatellites for stock identification applications was also evaluated. Variation at 14 loci was surveyed in approximately 26,000 Pacific herring from 90 sampling locations. Estimates of the genetic differentiation index FST by locus varied between 0.000 and 0.014, and the mean across all loci was 0.003. Four stocks of Pacific herring were defined in British Columbia, and stocks were also identified in southeast Alaska, Washington, and California. In British Columbia, differences in timing of spawning are the main isolating mechanisms among stocks, although geographic isolation of the spawning populations may also have some effect in maintaining the genetic distinctiveness of each stock. The limited genetic differentiation among Pacific herring populations in British Columbia is consistent with among‐population straying rates that are sufficient to homogenize allele frequencies over broad areas. Analysis of simulated mixtures from fishery sampling suggested that acceptable estimates of stock composition were achieved by use of the microsatellites. Mixed‐stock samples (∼1,700 individuals) were collected during research vessel surveys from 14 locations in British Columbia. Analysis of summer mixed‐stock samples from the Strait of Georgia and adjacent waters indicated that resident fish on the west side of the strait were mainly derived from primary‐spawning populations (i.e., those that spawned during the primary period in March) that failed to migrate to traditional summer feeding grounds. On the east side of the strait, Pacific herring of mainland inlet origin were found in higher proportions and presumably did not move in appreciable numbers to feeding areas off the west coast of Vancouver Island. In northern British Columbia, fish from northern late‐spawning populations dominated fishery samples collected in waters adjacent to the mainland until the end of June; however, by late July, this group had been replaced almost entirely by primary‐spawning Pacific herring of British Columbia origin.

Temporal and spatial variability in settlement and recruitment of echinoderms in kelp beds and barrens in Nova Scotia

Settlement and recruitment of echinoderms were measured in 2 adjacent habitats: a kelp bed (Laminaria longicruris) and an echinoid (Strongylocentrotus droebachiensis)-dominated barren ground at each of 2 sites in the rocky subtidal zone (5 to 10 m depth) off Nova Scotia. Settle- ment was measured using artificial collectors made of 0.05 m 2 panels of plastic turf that were deployed 0.2 m (low) and 2.3 m (high) above the bottom in each habitat, and sampled bi-weekly from June to November 1992 to 1994. Distinct settlement pulses of ophiuroids (Ophiopholis aculeata and Ophiura spp.), asteroids (Asterias spp.) and an echinoid (S. droebachiensis) occurred between July and September of each year at both sites. Timing of settlement differed consistently among species in relation to differences in timing of spawning and larval development. The magnitude of each pulse varied between years and species, and the year of maximum settlement differed between species, suggesting that species-specific processes regulate settlement rather than general environmental conditions. Settlement of all species was greater at the more protected site, but between-habitat pat- terns were not consistent among species. Asteroids settled in greater numbers in and above kelp beds, whereas ophiuroids showed a trend toward greater settlement in the barrens. The echinoid S. droebachiensis also tended to settle more in barrens, although the difference was not statistically sig- nificant. This suggests that kelp beds do not exhibit a consistent or strong effect on settlement. Sam- pling settlement concurrently at different frequencies (3 to 48 d) gave different estimates of settle- ment, indicating a need for assessment of sampling artifacts (e.g. changes in collector quality, post-settlement mortality or migration) that can occur over longer deployment intervals. For most species sampled, settlement predicted recruit density in natural populations the following year. How- ever, the strength of the relationship varied between species, probably because of differing post- settlement processes.