Abstract
Background
Understanding connectivity is critical to the management of exploited fish stocks, but migratory dynamics of Pacific halibut (
Hippoglossus stenolepis
) in the Bering Sea and ...Aleutian Islands region are not well-understood. In the current study, 145 Pacific halibut ≥ 82 cm fork length were tagged with Pop-up Archival Transmitting (PAT) tags to evaluate interannual dispersal, seasonal migration, and depth-specific habitat use.
Results
Endpoint locations obtained after 1 year at liberty (
n
= 79), fishery recoveries after 2–3 years at liberty (
n
= 5), and at-liberty geopositions based on light data (
n
= 5313 estimates from 109 fish) indicated geographically distinct movement patterns: Pacific halibut tagged in the Western and Central Aleutian Islands remained within the island groups in which the fish had been tagged; fish in the eastern Bering Sea remained in that ocean basin, moving among International Pacific Halibut Commission (IPHC) regulatory areas and into Russian waters; those tagged south of Unimak Pass in IPHC Regulatory Area 4A displayed the greatest amount of emigration, dispersing eastward both seasonally and interannually to as far south as Washington State. Analysis of daily maximum depth and temperature data from 113 individuals demonstrated group-level variation in summer temperatures experienced by the fish and in the timing, duration, and synchrony of movement to deep-water wintering grounds.
Conclusions
Depth-specific habitat use was suggestive of regionally explicit migratory contingents, while interannual dispersal patterns were consistent with the existence of multiple functional spawning units. The results may guide future research to examine cross-basin connectivity in the Northern Bering Sea and provide inputs for numerical modelling of individual movements, larval advection, and recruitment analyses.
Abstract
Characterizing migratory behaviours contributes to the sustainable management of marine fishes by resolving stock structure and identifying the timing and locations of events within fish ...life cycles. The migratory behaviour of Atlantic halibut (Hippoglossus hippoglossus) in the Gulf of St. Lawrence (GSL), Canada was characterized over an annual cycle using pop-up satellite archival tags (n = 15). Daily probability density functions of individual halibut positions were estimated using a geolocation model specifically developed to track demersal fish species in the GSL. Reconstructed migration routes (n = 8) revealed that Atlantic halibut displayed seasonal migrations, moving from deeper offshore waters in the winter to shallower nearshore waters in the summer. Variability in migratory behaviours was observed among individuals tagged at the same location and time. One individual resided year round in the vicinity of the tagging site, three individuals displayed homing behaviour, and four individuals did not return to the tagging site. The identification of presumed spawning rises for two individuals suggested that spawning of Atlantic halibut occurred in the GSL. Although based on a limited number of individuals, these results suggest that Atlantic halibut in the GSL forms a philopatric population, supporting the current separate management of this stock from the adjacent Scotian Shelf and southern Grand Banks stock.
Background Movement data represent important inputs to both numerical and conceptual models that contribute to the assessment and management of sablefish (Anoplopoma fimbria) and Pacific halibut ...(Hippoglossus stenolepis) in the eastern North Pacific. While conventional mark-recovery data have greatly increased our understanding of these populations, tagging methods that produce only endpoint data (i.e., locations at tagging and recapture) cannot address dynamics such as the timing, frequency, and recurrence of movements. As a preliminary step in evaluating the feasibility of using acoustic biotelemetry for addressing management-relevant questions for relatively deepwater (less than or equai to 600 m depth) species, we conducted tests of the detection range between VEMCO V16-5H transmitters and VR2W receivers. Six range-test stations were established that varied from a relatively shallow (154 m), narrow (3.8 km) ocean pass; through the mouth of a wide (20 km), deep (600 + m) fjord; and over the continental shelf. Each station consisted of one receiver mooring and five transmitter moorings deployed at regular distances from 200 to 1200 m from the base of the receiver mooring. Bottom depth varied from 195 to 588 m. Transmitters were suspended 0.5 and 5 m off bottom, and receivers at 145-400 m below the sea surface depend on bottom depth. Receivers were deployed for 162-595 days; however, maximum transmission time was 365 days. Results The rate at which acoustic transmissions were detected by the receivers decreased with distance from the transmitters, mostly monotonically; at first gradually, from transmitters at distances of 400-800 m from the receivers, and then more steeply at distances beyond 800 m. Considerable variability in detection rates was observed, including low detection rates from individual locations and distances. Temporal changes in detection rates were observed that included convergence/divergence between detection of transmitters at a given distance from receivers but that were suspended at different elevations above bottom; stepwise seasonal shifts in mean detection; diurnal periodicity that was likely due to diurnal winds; and tidally mediated detection cycles. We determined that a linear "gate" of receivers spaced 1000 m apart would have a very high probability (greater than or equai to 0.99) under most conditions of detecting an acoustically tagged Pacific halibut transiting the gate, and that tagged-halibut identification rates using 2400-m receiver spacing could approach or exceed 90%. However, during episodic periods of relatively poor tag detection, these rates are likely to decline to ~ 60-80%; and to below 10% under extreme conditions. Conclusions Acoustic telemetry is a feasible technique for monitoring the movement of deepwater epibenthic fishes. However, temporal and spatial variability in detection rates, especially in seasonally stratified waters, has a strong potential to impart biases on study results and generate spurious patterns unrelated to tagged-fish behavior. The nature of such biases should be carefully considered during array placement and data interpretation. Range testing should be conducted at all geographic locations at which arrays are to be established, rather than extrapolating from a few test locations. Arrays should always contain sentinel tags to monitor detection rates and account for transient features that affect those rates. We also note the necessity of placing at least two gates at any given location in order to substantiate movement of tagged animals past any desired point of reference. Keywords: Fish, Marine, Telemetry, Stationary acoustics, Detection range, Deepwater
Loher, T. 2011. Analysis of match–mismatch between commercial fishing periods and spawning ecology of Pacific halibut (Hippoglossus stenolepis), based on winter surveys and behavioural data from ...electronic archival tags. – ICES Journal of Marine Science, 68: 2240–2251. The fishery for halibut (Hippoglossus stenolepis) in the eastern Pacific is closed during the boreal winter, roughly corresponding to the seasonal spawning of the species. Opening and closing dates for each season are stipulated annually based on economics and biology. Historical surveys and data from electronic tags are analysed to assess the extent to which recent closures have encompassed the annual spawning cycle of the species, as defined by migration to offshore spawning sites, active spawning, and return to feeding areas. These were assessed by calculating mean maximum daily depth profiles for fish exhibiting seasonal migration, calculating the date-specific proportions of the tagged population either migrating to or resident on their feeding or spawning grounds, and examining the temporal distribution of spent and running fish in historical surveys along with evidence of spawning contained in high-resolution tag data. The data indicate that fishery closures over the past 20 years have been consistently too short to protect the entirety of a migration period that begins as early as September and is not substantially completed until May. Additionally, some recent season openings have encroached on the active spawning season. Failure to fully protect spawning migrations may allow seasonal interception fisheries, and the selective removal of early and late spawners could cause changes in stock demographics, restrict effective spawning, and influence long-term stock productivity, especially in the face of environmental variability.
The discovery of genetic markers linked to physiological traits in wild populations is increasingly desired for ecological and evolutionary studies, as well as to inform management decisions. ...However, identifying such markers often requires a large investment of both time and money. Serendipitously, in a recent microsatellite survey, we discovered three out of 16 microsatellite loci that were correlated to the female sex in Pacific halibut (Hippoglossus stenolepis). These three loci were screened in 550 Pacific halibut to determine their accuracy at identifying sex. Genetic assignment successfully identified sex in 92% of individuals from sample collections spanning 3,000 km and 9 years. All but two of 287 females had one copy of a characteristic allele for at least one of the three microsatellite loci, resulting in consistent heterozygote excess in females. This pattern is consistent with the hypothesis that females are the heterogametic sex in Pacific halibut, which thus may have a different sex-determination pattern than the closely related Atlantic halibut (Hippoglossus hippoglossus). A rapid divergence of sex-determining mechanisms could be either a cause or consequence of speciation between Pacific and Atlantic halibut. In either case, the ability to genetically identify sex in individual Pacific halibut provides a new tool for ecological studies, fisheries management, and insight into the evolution of sex determination in flatfish.
Fisheries for Pacific halibut (Hippoglossus stenolepis) in the US Pacific Northwest support a variety of harvest sectors including some that are restricted to coastal offshore waters and others ...confined to the inland waters of the Salish Sea. Such restrictions have generated interest in the degree to which the Salish Sea represents an extension of the offshore population versus its potential to support an isolated stock. Here, twelve female Pacific halibut were tagged during boreal summer with pop-up archival transmitting (PAT) tags that were programmed to report during either the subsequent winter spawning period or late-spring feeding period. High-resolution depth data failed to produce evidence of spawning within the Salish Sea, while depth-temperature profiles were consistent with the departure of migrants between October and January. Final positions and at-liberty longitude estimates suggest that ~60% of the tagged fish departed the Salish Sea, with confirmed migrations to Canada and Alaska. The recapture in the southern Salish Sea of one fish whose tag had reported earlier from offshore Canadian waters demonstrated the occurrence of cyclic migrations. Evaluation of likely maturity status suggests that local demographics reflect either the cumulative effects of spawning migrations in which some emigrants remain offshore after departing the system, or some combination of enhanced growth or delayed maturity. These findings confirm that the Salish Sea does not represent a functionally-independent stock, but suggest that inshore waters may play a unique role by receiving recruits, rearing individuals to maturity, and exporting spawners to the offshore stock components, while retaining a proportion of site-faithful individuals with cyclic seasonal connectivity with offshore spawning groups.
•Connectivity in Pacific halibut was examined between the Salish Sea and offshore waters.•Maturity-at-length appears to be lower in the Salish than offshore.•Female halibut moved from the Salish Sea to deep offshore waters during the spawning season.•Emigrants were found to both remain offshore and return to the Salish the following spring.•Partial migration was apparent: some individuals failed to depart and others did so only transiently.
•We model and compare four bomb-produced Δ14C curves from the North Pacific Ocean.•Bayesian analysis and Markov chain Monte Carlo simulation is used.•The Gulf of Alaska and eastern Bering Sea have ...unique bomb-produced Δ14C curves.•Ages estimated for the fish yellowfin sole and northern rockfish are accurate.•Probabilities of age bias (error) for yellowfin sole and northern rockfish is small.
Fish age validation with bomb-produced radiocarbon (14C) requires a known-age Δ14C reference chronology spanning the era of a marine increase in bomb-produced 14C (1950s to 1960s). Concordance between otolith Δ14C in a validation sample and the reference chronology indicates accurate test ages. Here, we present an information-theoretic approach to hypothesis testing and use Bayesian data analysis with Markov chain Monte Carlo simulation as a probabilistic framework to quantitatively estimate age determination bias and its uncertainty. Using this approach, we compare a new Δ14C reference chronology from the eastern Bering Sea and a previously established reference from the Gulf of Alaska with otolith Δ14C in two validation species, eastern Bering Sea yellowfin sole (Limanda aspera) and Gulf of Alaska northern rockfish (Sebastes polyspinis). Our goals were twofold: (i) to validate the age determination methods for northern rockfish and yellowfin sole using comparisons within oceanic basins, and (ii) to explore the outcome of making naïve comparisons of these validation data sets to reference chronologies across oceanic basins. Based on within-basin comparisons we concluded that estimated ages for eastern Bering Sea yellowfin sole and Gulf of Alaska northern rockfish were accurate. We further concluded that there were important differences in otolith 14C uptake between fish from the two ocean basins.
Background The effects of temporal data resolution on the interpretation of fish behaviours are questions fundamental to research programs using electronic tags with finite data storage and data ...transmission capacities. However, understanding these effects requires sub-sampling high-resolution data at multiple temporal resolutions. In pop-up satellite archival tags (PSATs), data transmissions via satellite are limited, so temporal resolution is a decreasing function of the deployment duration. Physical recovery of PSATs overcomes this limitation, providing data on temperature, depth, etc., at rates at least 15-30 times greater than transmitted data. Results Using PSATs physically recovered from Atlantic halibut (Hippoglossus hippoglossus), we evaluated the effects of data resolution (2, 30, 60 min) on interpreting vertical movements including rapid ascents during the expected spawning season. Putative ‘spawning rises’ of 6-20 min were only present within highest temporal resolution data. Vertical movement rates during spawning rises identified with high-resolution data exceeded rates in all other periods; such movement rates were virtually absent in all other tagged fish within the spawning period. Mean maximum ascent rates were 13 and 23 times higher when the sampling interval was 2 versus 30 or 60 min, respectively. Conclusions We illustrate the limitations of using satellite-transmitted data to quantify vertical movement rates and detect potential spawning events in marine teleosts. Such low temporal resolution data suggest spurious results by masking important behaviours that archived data reveal as occurring at high frequencies. We highlight new technologies that facilitate PSAT recoveries at sea to overcome these limitations and facilitate analyses of high-frequency archived data.
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