Kelp Rockfish Research Articles

Site fidelity, vertical movement, and habitat use of nearshore reef fishes on offshore petroleum platforms in southern California

Off California, economically important nearshore reef fishes inhabit the shallow (<20 m) regions of offshore petroleum platforms on the San Pedro Shelf (SPS). It is essential to understand the degrees to which platforms support fish over time to indicate whether biological requirements (e.g., shelter, diet, reproduction) are being met. To determine the ecological importance of platforms as fish habitat, the site fidelity and depth/habitat use of adult cabezon, Scorpaenichthys marmoratus (Ayres, 1854), grass rockfish, Sebastes rastrelliger (Jordan and Gilbert, 1880), kelp rockfish, Sebastes atrovirens (Jordan and Gilbert, 1880), and California sheephead, Semicossyphus pulcher (Ayres, 1854) were investigated at platforms Edith (50 m bottom depth) and Eureka (212 m). A total of 63 fish were acoustically tagged and monitored for up to 578 d. Sixty-three percent of individuals were still present at platforms at the end of the study (long-term site fidelity), with 55 individuals detected a mean of 66.9% (SD 36.0%) of their total days at liberty (daily site fidelity). All species displayed a shift in seasonal depth use. The shallowest horizontal level, consisting of various horizontal beams at platform Edith (15 m depth) and Eureka (17 m), was the most utilized habitat by grass rockfish, kelp rockfish, and California sheephead. Cabezon at platform Eureka utilized depths (21–31 m) unassociated with horizontal levels, while at platform Edith they primarily utilized the second horizontal level (30 m). Decommissioning options that remove the shallowest 26 m of structure would eliminate the habitat most utilized by three of the four study species that dominate the nearshore reef fish communities at SPS platforms.

Dispersal of a nearshore marine fish connects marine reserves and adjacent fished areas along an open coast.

Marine species with pelagic larvae typically exhibit little population structure, suggesting long-distance dispersal and high gene flow. Directly quantifying dispersal of marine fishes is challenging but important, particularly for the design of marine protected areas (MPAs). Here, we studied kelp rockfish (Sebastes atrovirens) sampled along ~25km of coastline in a boundary current-dominated ecosystem and used genetic parentage analysis to identify dispersal events and characterize them, because the distance between sedentary parents and their settled offspring is the lifetime dispersal distance. Large sample sizes and intensive sampling are critical for increasing the likelihood of detecting parent-offspring matches in such systems and we sampled more than 6,000 kelp rockfish and analysed them with a powerful set of 96 microhaplotype markers. We identified eight parent-offspring pairs with high confidence, including two juvenile fish that were born inside MPAs and dispersed to areas outside MPAs, and four fish born in MPAs that dispersed to nearby MPAs. Additionally, we identified 25 full-sibling pairs, which occurred throughout the sampling area and included all possible combinations of inferred dispersal trajectories. Intriguingly, these included two pairs of young-of-the-year siblings with one member each sampled in consecutive years. These sibling pairs suggest monogamy, either intentional or accidental, which has not been previously demonstrated in rockfishes. This study provides the first direct observation of larval dispersal events in a current-dominated ecosystem and direct evidence that larvae produced within MPAs are exported both to neighbouring MPAs and to proximate areas where harvest is allowed.

Microhaplotypes provide increased power from short‐read DNA sequences for relationship inference

The accelerating rate at which DNA sequence data are now generated by high-throughput sequencing instruments provides both opportunities and challenges for population genetic and ecological investigations of animals and plants. We show here how the common practice of calling genotypes from a single SNP per sequenced region ignores substantial additional information in the phased short-read sequences that are provided by these sequencing instruments. We target sequenced regions with multiple SNPs in kelp rockfish (Sebastes atrovirens) to determine "microhaplotypes" and then call these microhaplotypes as alleles at each locus. We then demonstrate how these multi-allelic marker data from such loci dramatically increase power for relationship inference. The microhaplotype approach decreases false-positive rates by several orders of magnitude, relative to calling bi-allelic SNPs, for two challenging analytical procedures, full-sibling and single parent-offspring pair identification. We also show how the identification of half-sibling pairs requires so much data that physical linkage becomes a consideration, and that most published studies that attempt to do so are dramatically underpowered. The advent of phased short-read DNA sequence data, in conjunction with emerging analytical tools for their analysis, promises to improve efficiency by reducing the number of loci necessary for a particular level of statistical confidence, thereby lowering the cost of data collection and reducing the degree of physical linkage amongst markers used for relationship estimation. Such advances will facilitate collaborative research and management for migratory and other widespread species.

Whole-Body Concentrations of Elements in Three Fish Species from Offshore Oil Platforms and Natural Areas in the Southern California Bight, USA

There is concern that offshore oil platforms off Southern California may be contributing to environmental contaminants accumulated by marine fishes. To examine this possibility, 18 kelp bass (Paralabrax clathratus Girard, 1854), 80 kelp rockfish (Sebastes atrovirens Jordan and Gilbert, 1880), and 98 Pacific sanddab (Citharichthys sordidus Girard, 1854) were collected from five offshore oil platforms and 10 natural areas during 2005-2006 for whole-body analysis of 63 elements. Forty-two elements were excluded from statistical comparisons as they (1) consisted of major cations that were unlikely to accumulate to potentially toxic concentrations; (2) were not detected by the analytical procedures; or (3) were detected at concentrations too low to yield reliable quantitative measurements. The remaining 21 elements consisted of aluminum, arsenic, barium, cadmium, chromium, cobalt, copper, gallium, iron, lead, lithium, manganese, mercury, nickel, rubidium, selenium, strontium, tin, titanium, vanadium, and zinc. Statistical comparisons of these elements indicated that none consistently exhibited higher concentrations at oil platforms than at natural areas. However, the concentrations of copper, selenium, titanium, and vanadium in Pacific sanddab were unusual because small individuals exhibited either no differences between oil platforms and natural areas or significantly lower concentrations at oil platforms than at natural areas, whereas large individuals exhibited significantly higher concentrations at oil platforms than at natural areas.

Spatial pattern of natal signatures in the otoliths of juvenile kelp rockfish along the Californian coast

The natal origin of a post-dispersal marine fish may be determined by examining the trace elemental signatures present in the core (i.e. the pre-dispersal region) of the otolith. We found distinct spatial differences in the natal elemental signatures in the core region of the otoliths of post- dispersal juvenile kelp rockfish Sebastes atrovirens collected along the coast of California, USA. Laser ablation inductively coupled plasma mass spectrometry of individual otolith cores revealed detectable levels of Mn, Mg, Ba, and Sr. Using a Bayesian classification model, 2 unique elemental signature types were identified in both 2001 and 2002, and the signatures were chemically similar across years. In both years, locations received a mixture of natal types ('A' and 'B'), indicating the con- tribution of at least 2 chemically distinct sources to recruitment. The spatial pattern of the natal types varied among sites for both years. In 2001, Type A was nearly absent from the northernmost location, suggesting a southern origin and a limitation in the dispersal and contribution of this chemically iden- tified natal type. In 2002, most locations had a mix of Types A and B, but Type A was most abundant in the south and least abundant in the central part of the spatial domain. However, it was not possible to specify the full extent of dispersal of either natal type. We demonstrated use of elemental signa- tures in the otolith core of post-dispersal individuals to evaluate larval dispersal patterns which may document the extent to which kelp rockfish populations along the California coast receive recruits from different chemically distinct sources.

Realized and potential larval connectivity in the Southern California Bight

Populations of many nearshore marine species are connected through the dispersal of their larvae. In this paper, larval connectivity patterns in the Southern California Bight are explored using 2 quantities: potential and realized larval connectivity. Potential connectivity is defined as the probability of larval transport from a source to a destination location and is quantified using Lagrangian particle simulations. Realized connectivity is the product of potential connectivity with larval production and can be used to estimate larval settlement patterns. Potential and realized con- nectivity patterns are quantified for kelp bass Paralabrax clathratus, kelp rockfish Sebastes atro- virens, and red abalone Haliotis rufescens, 3 species with a range of larval dispersal characteristics. Connectivity patterns were found to be both heterogeneous, with locations having different source and destination strengths, and asymmetric, with directionality in larval transport. Both potential and realized connectivity were strongly influenced by the length and timing of the spawning season as well as planktonic larval duration. For kelp bass and kelp rockfish, a strong correspondence was found between realized and potential destination locations, suggesting that circulation processes have a dominant role in shaping the spatial distribution of these 2 species. Strong temporal variabil- ity in realized larval connectivity was observed on seasonal and inter-annual time scales (particularly between El Nino and La Nina conditions). These results provide novel information for use in marine fisheries and conservation management.

Maternal effects in rockfishes Sebastes spp.: a comparison among species

In temporally variable environments, longevity is generally considered to be a bet- hedging adaptation in which reproductive effort is spread across many years, increasing the proba- bility that favorable conditions for larvae will be encountered at least some time in a female's life span. A long reproductive life span provides the potential for individual females to exhibit inter- annual differences in energy allocation patterns that may be age- or size-dependent. We examine the effects of maternal age and size on larval quality, fecundity, and timing of parturition in 5 species of live-bearing rockfishes in the genus Sebastes (blue, yellowtail, olive, gopher, and kelp rockfish), and compare these maternal effects with previously documented patterns in black rockfish Sebastes melanops. Larval quality was indexed by size (notochord length) and condition (lipid storage in the oil globule). Maternal effects were found for oil globule size in blue, yellowtail and gopher rockfish, for weight-specific fecundity in blue and yellowtail rockfish, and for parturition date in blue, yellow- tail, and kelp rockfish. In all cases the maternal effects were similar to those reported for black rock- fish, with increasing lipid provisioning of larvae, greater weight-specific fecundity, and earlier timing of parturition in the spawning season with increasing maternal age or size. No effect of maternal age or size on larval size was observed. In general, maternal effects were more evident in winter spawn- ing species of the subgenus Sebastosomus (black, blue, olive, and yellowtail rockfish) than the spring spawning species of the subgenus Pteropodus (gopher and kelp rockfish). These results confirm that older and larger females in rockfish populations may contribute disproportionately to larval recruit- ment by producing higher quality larvae and more larvae per unit biomass, and releasing them at a different time than younger and smaller females. A shift in timing of parturition with female age may constitute a diversified bet-hedging strategy, providing a temporal spread of spawning effort within a maternal lineage, whereby successive female progeny release larvae at different times within the same year.

Use of otolith natal elemental signatures as natural tags to evaluate connectivity among open-coast fish populations

Variation of trace elemental composition in fish otoliths has been successfully used to reconstruct the environmental history of fish, including the movement of early life stages among populations and habitats. Past studies have focused primarily on estuarine-dependent species, and information has been very limited for species that spawn along open coastlines, where spawning locations are not discrete and environmental gradients are less extreme. In this study, we used defined natal otolith elemental signatures from pre-pelagic larvae of the viviparous kelp rockfish Sebastes atrovirens taken from the natal source along the open coast of California and the offshore Channel Islands to identify the dispersal patterns of recently recruited individuals from the Channel Islands. Using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), we chemically analyzed the otolith core (the portion of the otolith corresponding to the period of time prior to larval release) of recruits and compared the elemental signatures to spatially restricted natal otolith elemental signatures in southern California. Linear discriminant function analysis (DFA) revealed that the natal elemental signature of the mainland California location was not apparent in the elemental signatures of Channel Island recruit cores, suggesting a lack of exchange among the locations for the recruitment year. Several recruits had core elemental signatures that differed from all defined natal locations, suggesting that they originated from an uncharacterized site. These data demonstrate the use of natal otolith chemical data within a limited geographic area to identify larval dispersal patterns, with particular focus on sources that do not contribute to the defined locations.

Multiple paternity in viviparous kelp rockfish, Sebastes atrovirens

Analysis of multilocus microsatellite genotypes revealed multiple paternity for all of the seven viable broods of larvae produced by kelp rockfish, Sebastes atrovirens (Jordan and Gilbert 1880), held jointly in a large aquarium tank (n = eight females and eight males). Only two of the eight experimental males were identified as fathers, and alleles not found in any of the captive males were present in all seven broods, demonstrating paternity by wild males external to the experiment. Thus, all of the females mated with one or more males prior to capture, confirming that female kelp rockfish are capable of storing sperm and controlling the overall timing of egg fertilization. These results highlight the potential for a paternal influence on larval quality through female mate choice and sperm competition.

Temporal recruitment patterns and gene flow in kelp rockfish (Sebastes atrovirens)

Pelagic dispersal of marine organisms provides abundant opportunity for gene flow and presumably inhibits population genetic divergence. However, ephemeral, fine-scale, temporal and spatial genetic heterogeneity is frequently observed in settled propagules of marine species that otherwise exhibit broad-scale genetic homogeneity. A large variance in reproductive success is one explanation for this phenomenon. Here, genetic analyses of 16 microsatellite loci are used to examine temporal patterns of variation in young-of-year kelp rockfish (Sebastes atrovirens) recruiting to nearshore habitat in Monterey Bay, California, USA. Population structure of adults from central California is also evaluated to determine if spatial structure exists and might potentially contribute to recruitment patterns. Genetic homogeneity was found among 414 young-of-year sampled throughout the entire 1998 recruitment season. No substantial adult population structure was found among seven populations spanning 800 km of coastline that includes the Point Conception marine biogeographic boundary. Comparison of young-of-year and adult samples revealed no genetic differentiation and no measurable reduction in genetic variation of offspring, indicating little variance in reproductive success and no reduction in effective population size for this year class. Simulation analyses determined that the data set was sufficiently powerful to detect both slight population structure among adults and a small reduction in effective number of breeders contributing to this year class. The findings of high gene flow and low genetic drift have important implications for fisheries management and conservation efforts.

DENSITY DEPENDENCE IN MARINE FISH POPULATIONS REVEALED AT SMALL AND LARGE SPATIAL SCALES

Experimental manipulation of population density has frequently been used to demonstrate demographic density dependence. However, such studies are usually small scale and typically provide evidence of spatial (within-generation) density dependence. It is often unclear whether small-scale, experimental tests of spatial density dependence will accurately describe temporal (between-generation) density dependence required for population regulation. Understanding the mechanisms generating density dependence may provide a link between spatial experiments and temporal regulation of populations. In this study, I manipulated the density of recently settled kelp rockfish (Sebastes atrovirens) in both the presence and absence of predators to test for density-dependent mortality and whether predation was the mechanism responsible. I also examined mortality of rockfish cohorts within kelp beds throughout central California to evaluate temporal (between-generation) density dependence in mortality. Experiments suggested that short-term behavioral responses of predators and/or a shortage of prey refuges caused spatial density dependence. Temporal density dependence in mortality was also detected at larger spatial scales for several species of rockfish. It is likely that short-term responses of predators generated both spatial and temporal density dependence in mortality. Spatial experiments that describe the causal mechanisms generating density dependence may therefore be valuable in describing temporal density dependence and population regulation.

Behavioral ecology of young-of-the-year kelp rockfish, Sebastes atrovirens Jordan and Gilbert (Pisces: Scorpaenidae).

Young-of-the-year (YOY) kelp rockfish, Sebastes atrovirens, recruit initially to the canopy of the giant kelp, Macrocystis pyrifera (L.), along the coast of central California. During the summer of 1991, I observed major fluctuations in YOY kelp rockfish abundance in the canopy before the onset of a vertical migration downward to the Macrocystis holdfasts. Within the Macrocystis canopy, YOY kelp rockfish make a series of microhabitat shifts preparatory to their downward migration, forming smaller and more closely held aggregations. Experimental manipulations of Macrocystis architecture indicate that YOY kelp rockfish densities are reduced in areas with only small Macrocystis (few stipes) compared to unmanipulated areas with a range of Macrocystis sizes. Unusually large Macrocystis, created by binding multiple kelps together, did not compensate for a preponderance of small Macrocystis in the surrounding areas. In unmanipulated habitat, YOY kelp rockfish densities were correlated with the size of the Macrocystis (number of stipes). Habitat selection in the canopy and holdfasts appears to be behavioral and is closely tied to the architecture of the alga. The onset of the downward migration appears to be triggered by a combination of ontogenetic and environmental cues.

Geographic Variation in the Occurrence of Tympanic Spines and Possible Genetic Differentiation in the Kelp Rockfish (Sebastes atrovirens)

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