Post-release Mortality Research Articles

How Much Hatchery-Reared Brown Trout Move in a Large, Deep Subalpine Lake? An Acoustic Telemetry Study

Fish movement into large, deep lakes has been rarely investigated due to the complexity and extent of such ecosystems. Among the different monitoring methods available, acoustic telemetry enables the study of the spatial ecology and behavior of aquatic organisms in lentic environments. In this study, the movement of 69 hatchery-reared adult brown trout (size 43–61 cm) marked with acoustic transmitters was monitored in the large and deep subalpine Lake Lugano (Switzerland and Italy). Trout were tracked for six consecutive months by seven acoustic receivers (March–August 2022), positioned in a non-overlapping array. Trout movement was reconstructed using R packages specific for acoustic telemetry (actel and RSP), which also allowed us to translate tracking information into utilization distribution (UD) areas for each fish. The effects of different environmental variables (rainfall, water discharge of the two main tributaries of Lake Lugano, atmospheric pressure, cloud coverage, and moon phases) on trout movement were tested, but none of these variables seemed to significantly correlate with fish movement. After release, most of the tagged fish exhibited reiterative movements during the initial month, with some maintaining this behavior throughout the entire study period. This spatial behavior can be particularly evident in hatchery-reared fish due to their aggressive and bold attitude. The association of these behavioral traits, shaped by domestication, could expose hatchery-reared fish to high risks and post-release mortality in the wild. Indeed, within a few months after the release, most of the tagged fish were no longer detected by the acoustic receivers. In addition, 26% of the total tagged fish were caught by recreational or professional fishermen.

Aerial Systems for Releasing Natural Enemy Insects of Purple Loosestrife Using Drones

Lythrum salicaria (purple loosestrife) is an invasive species that displaces native wetland flora in the USA. The detection and manual release of biological control agents for L. salicaria is challenging because L. salicaria inhabits many inaccessible areas. This study was conducted to develop aerial systems for the detection of L. salicaria and the release of its natural enemy, Galerucella calmariensis (Coleoptera: Chrysomelidae). We determined the optimal sensors and flight height for the aerial detection of L. salicaria and designed an aerial deployment method for G. calmariensis. Drone-based aerial surveys were conducted at various flight heights utilizing RGB, multispectral, and thermal sensors. We also developed an insect container (i.e., bug ball) for the aerial deployment of G. calmariensis. Our findings indicated that L. salicaria flowers were detectable with an RGB sensor at flight heights ≤ 15 m above the canopy. The post-release mortality and feeding efficiency of G. calmariensis did not significantly differ from the control group (non-aerial release), indicating the feasibility of the targeted release of G. calmariensis. This innovative study establishes a critical foundation for the future development of sophisticated aerial systems designed for the automated detection of invasive plants and the precise release of biological control agents, significantly advancing ecological management and conservation efforts.

Medicaid Expansion and Mortality Among Persons Who Were Formerly Incarcerated

Since 2014, Medicaid expansion has been implemented in many states across the US, increasing health care access among vulnerable populations, including formerly incarcerated people who experience higher mortality rates than the general population. To examine population-level association of Medicaid expansion with postrelease mortality from all causes, unintentional drug overdoses, opioid overdoses, polydrug overdoses, suicides, and homicides among formerly incarcerated people in Rhode Island (RI), which expanded Medicaid, compared with North Carolina (NC), which did not expand Medicaid during the study period. A cohort study was conducted using incarceration release data from January 1, 2009, to December 31, 2018, linked to death records from January 1, 2009, to December 31, 2019, on individuals released from incarceration in RI and NC. Data analysis was performed from August 20, 2022, to February 15, 2024. Participants included those aged 18 years or older who were released from incarceration. Individuals who were temporarily held during ongoing judicial proceedings, died during incarceration, or not released from incarceration during the study period were excluded. Full Medicaid expansion in RI effective January 1, 2014. Mortality from all causes, unintentional drug overdoses, unintentional opioid and polydrug overdoses, suicides, and homicides. Between 2009 and 2018, 17 824 individuals were released from RI prisons (mean [SD] age, 38.39 [10.85] years; 31 512 [89.1%] male) and 160 861 were released from NC prisons (mean [SD] age, 38.28 [10.84] years; 209 021 [87.5%] male). Compared with NC, people who were formerly incarcerated in RI experienced a sustained decrease of 72 per 100 000 person-years (95% CI, -108 to -36 per 100 000 person-years) in all-cause mortality per quarter after Medicaid expansion. Similar decreases were observed in RI in drug overdose deaths (-172 per 100 000 person-years per 6 months; 95% CI, -226 to -117 per 100 000 person-years), including opioid and polydrug overdoses, and homicide deaths (-23 per 100 000 person-years per year; 95% CI, -50 to 4 per 100 000 person-years) after Medicaid expansion. Suicide mortality did not change after Medicaid expansion. After Medicaid expansion in RI, non-Hispanic White individuals experienced 3 times greater sustained decreases in all-cause mortality than all racially minoritized individuals combined, while non-Hispanic Black individuals did not experience any substantial benefits. There was no modification by sex. Individuals aged 30 years or older experienced greater all-cause mortality reduction after Medicaid expansion than those younger than 30 years. Medicaid expansion in RI was associated with a decrease in all-cause, overdose, and homicide mortality among formerly incarcerated people. However, these decreases were most observed among White individuals, while racially minoritized individuals received little to no benefits in the studied outcomes.

Rates and causes of death after release from incarceration: an individual participant data meta-analysis from 1,471,526 people in eight high- and middle-income countries

BackgroundFormerly incarcerated people have exceptionally poor health profiles and are at increased risk of preventable mortality when compared to their general population peers. However, not enough is known about the epidemiology of mortality in this population – specifically the rates, causes, and timing in specific subgroups and regions – to inform the development of targeted, evidence-based responses. MethodsWe examined mortality outcomes for 1,471,526 people released from incarceration in eight countries from 1980-2018, across 10,534,441 person-years of follow-up (range: 0-24 years per person). We combined data from 18 cohort studies using two-step individual participant data meta-analyses to estimate pooled all-cause and cause-specific crude mortality rates (CMRs) per 100,000 person-years, with 95% confidence intervals (95%CI), for specific time periods after release, overall and stratified by age, sex, and region. Findings75,427 deaths were recorded. The all-cause CMR was highest during the first week. The highest cause-specific rates of death during the first week were due to alcohol and other drug poisoning, suicide, and cardiovascular disease. We observed considerable variation in cause-specific CMRs over time since release and across regions. Pooled all-cause CMRs were similar between males and females, and were higher in older age groups. InterpretationThe markedly elevated rate of death in the first week post-release underscores an urgent need for investment in evidence-based, coordinated transitional healthcare, including treatment for mental illness and substance use disorders. Variations in both rates and causes of death over time highlight the need for routine monitoring of post-release mortality.

The Effect of Incarceration on Mortality

Abstract This paper analyzes the effect of incarceration on mortality using administrative data from Ohio between 1992 and 2017. We first document that long-run survival is higher among the incarcerated than similar nonincarcerated defendants. Using event study designs centered around the time of release, we show why: mortality risk halves during the period of incarceration, with large reductions in murders, overdoses, and natural causes of death. However, incarceration does not increase postrelease mortality, and so the overall effect is increased longevity. These estimates reflect the high-risk environment faced by defendants when not incarcerated and suggest noncarceral policies to reduce these risks.

Multistage time-to-event models improve survival inference by partitioning mortality processes of tracked organisms

Advances in tagging technologies are expanding opportunities to estimate survival of fish and wildlife populations. Yet, capture and handling effects could impact survival outcomes and bias inference about natural mortality processes. We developed a multistage time-to-event model that can partition the survival process into sequential phases that reflect the tagged animal experience, including handling and release mortality, post-release recovery mortality, and subsequently, natural mortality. We demonstrate performance of multistage survival models through simulation testing and through fish and bird telemetry case studies. Models are implemented in a Bayesian framework and can accommodate left, right, and interval censorship events. Our results indicate that accurate survival estimates can be achieved with reasonable sample sizes (n≈100+)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$n\\approx 100+)$$\\end{document} and that multimodel inference can inform hypotheses about the configuration and length of survival stages needed to adequately describe mortality processes for tracked specimens. While we focus on survival estimation for tagged fish and wildlife populations, multistage time-to-event models could be used to understand other phenomena of interest such as migration, reproduction, or disease events across a range of taxa including plants and insects.

Rates and causes of death after release from incarceration among 1 471 526 people in eight high-income and middle-income countries: an individual participant data meta-analysis

Formerly incarcerated people have exceptionally poor health profiles and are at increased risk of preventable mortality when compared with their general population peers. However, not enough is known about the epidemiology of mortality in this population-specifically the rates, causes, and timing of death in specific subgroups and regions-to inform the development of targeted, evidence-based responses. We aimed to document the incidence, timing, causes, and risk factors for mortality after release from incarceration. We analysed linked administrative data from the multi-national Mortality After Release from Incarceration Consortium (MARIC) study. We examined mortality outcomes for 1 471 526 people released from incarceration in eight countries (Australia, Brazil, Canada, New Zealand, Norway, Scotland, Sweden, and the USA) from 1980 to 2018, across 10 534 441 person-years of follow-up (range 0-24 years per person). We combined data from 18 cohort studies using two-step individual participant data meta-analyses to estimate pooled all-cause and cause-specific crude mortality rates (CMRs) per 100 000 person-years, for specific time periods (first, daily from days 1-14; second, weekly from weeks 3-12; third, weeks 13-52 combined; fourth, weeks 53 and over combined; and fifth, total follow-up) after release, overall and stratified by age, sex, and region. 75 427 deaths were recorded. The all-cause CMR during the first week following release (1612 [95% CI 1048-2287]) was higher than during all other time periods (incidence rate ratio [IRR] compared with week 2: 1·5 [95% CI 1·2-1·8], I2=26·0%, weeks 3-4: 2·0 [1·5-2·6], I2=53·0%, and weeks 9-12: 2·2 [1·6-3·0], I2=70·5%). The highest cause-specific mortality rates during the first week were due to alcohol and other drug poisoning (CMR 657 [95% CI 332-1076]), suicide (135 [36-277]), and cardiovascular disease (71 [16-153]). We observed considerable variation in cause-specific CMRs over time since release and across regions. Pooled all-cause CMRs were similar between males (731 [95% CI 630-839]) and females (660 [560-767]) and were higher in older age groups. The markedly elevated rate of death in the first week post-release underscores an urgent need for investment in evidence-based, coordinated transitional healthcare, including treatment for mental illness and substance use disorders to prevent post-release deaths due to suicide and overdose. Temporal variations in rates and causes of death highlight the need for routine monitoring of post-release mortality. Australia's National Health and Medical Research Council.

Post‐release mortality of line‐caught snapper Chrysophrys auratus depends on hook site and capture depth

AbstractCatch‐and‐release angling is common in recreational fisheries, but post‐release mortality (PRM) may be high. We conducted a controlled field experiment to estimate mortality of released snapper Chrysophrys auratus. Recreational fishers caught 960 snapper from three depth strata (<15, 15–25, 26–40 m) that were either lip‐hooked, foul‐hooked or gut‐hooked. A bottom longline vessel caught 162 lip‐hooked fish in shallow water to serve as controls. Fish were held in 15‐m deep holding nets. All control fish and 80% of treatment fish survived, with anatomical hook site and capture depth significantly predicting mortality. Probability of mortality was lowest for lip‐hooked fish in shallow water (5 m = 0.00, 95% CI [0.00, 0.03]), but increased rapidly to 20 m (0.24, 95% CI [0.2, 0.3]). Mortality of foul‐hooked fish increased steadily with depth from 0.05 (95% CI [0.00, 0.78]) at 5 m to 0.65 (95% CI [0.13, 0.96]) at 40 m. Gut‐hooking resulted in high mortality at all depths but a low sample size resulted in high uncertainty of estimates. Our results indicate that snapper PRM can be reduced by fishing in shallow water and by mitigating gut‐hooking, possibly by using large circle hooks.

Anatomical hooking location and bleeding occurrence in northern pike (Esox lucius) caught in recreational catch-and-release angling in a lake with reduced prey fish availability

Catch-and-release (C&R) is a common practice in recreational angling for northern pike (Esox lucius), whereby the angler releases the fish back into the water after capture with the expectation that it will survive with negligible stress and physical injuries. This may not always be the case, as hooking in critical anatomical locations, such as gills, esophagus, and stomach, increases the frequency of bleeding at the hook wound and has been recognized as a key determinant of post-release mortality in pike. Several factors (e.g. bait type and size, hook characteristics, and fish length) can influence the risk of hooking in critical locations, and the fish’s willingness to strike the fishing lure/bait may largely depend on previous feeding history and associated motivation to feed. In this respect, food deprivation and greater feeding motivation can be expected to result in an intensified response and more forceful attacks on fishing lures/baits, which could increase the risk of hooking injuries in sensitive tissues, as the fish may ingest the hook more deeply. Here, we assess the hooking location and bleeding occurrence in pike caught on soft plastic shads and baitfish in a shallow eutrophic lake. The prey fish density of this lake, primarily common roach (Rutilus rutilus), has been substantially reduced by seining as part of a lake restoration project. Experimental angling sessions took place at the end of 2020 and 2022, approximately 1–2 months and 25–26 months after the initial reduction in prey fish density, respectively. Removal of roach from the lake was also done regularly by seining after the angling sessions in 2020. Pike angled in 2022 had significantly lower body condition than individuals caught in 2020, indicating that mass removal of roach from the lake resulted in food shortage. The risk of hooking in critical locations (herein defined as hooking in gills and back of mouth) was not associated to angling year, body condition, or length of the pike. However, across the two angling years, the incidence of hooking in critical locations was higher for soft plastic shads compared to baitfish (24.2% versus 7.4%). Pike caught on soft plastic shads also bled more frequently than individuals caught on baitfish (19.7% versus 6.2%), most likely due to the fact that hooking in the gills almost exclusively occurred with soft plastic shads. Bleeding propensity was also not related to angling year, body condition, or fish length. Hence, the present study found no evidence that long-term reductions in food availability and resulting declines in body condition influence how pike strike and ingest fishing lures/baits, at least not in a manner that increases the risk of hooking injuries in sensitive locations. Instead, bait type seems to play the largest role for the observed bleeding patterns. We recommend that future studies investigate the potential effects of C&R angling on the post-release survival of pike with reduced body condition due to limited food availability.

Mortality Among Individuals Released From U.S. Prisons: Does Military History Matter?

The physiological effects of imprisonment are well-documented and include a heightened risk for various forms of mortality post-release. The incarceration-mortality nexus does not apply equally to all groups, however, and research shows that some demographics (i.e., vulnerable populations) experience a greater likelihood of death. In the current study, we analyze correctional data over a 10-year period (2010–2019; n = 36,716) from Minnesota to assess the extent to which formerly incarcerated military veterans differ from non-veterans in their relative risk of mortality, net of relevant control variables. We also examine whether specific risk factors for post-release mortality differ between these groups. Findings indicate that veteran status is not a significant predictor of all-cause, natural, or unnatural mortality among releasees, though several notable within-group differences were observed. Policy implications of the current study are discussed in relation to the provision of veteran-centric health care services and directions for future research are given.

Trouble in the trawls: Is bycatch in trawl fisheries preventing the recovery of sawfish? A case study using the US population of smalltooth sawfish, Pristis pectinata

All five species of sawfish (Family Pristidae), are among the most threatened families of elasmobranchs, and face significant threats from fishing, in particular trawl fisheries, and habitat loss. Unfortunately, there is little data on the level of sawfish taken in trawl fisheries outside Australia and the United States and case studies from these areas can provide a “risk analysis” for populations elsewhere. In the United States, bycatch risk for smalltooth sawfish is significantly higher for the southeast shrimp trawl fishery than all other fisheries assessed. Using new estimates of life history and population size, an updated population viability model was developed and trajectories using different scenarios of initial population sizes, fishery catches and post-release mortality were projected for 100 years. The simulated population trajectories for the assumed initial population sizes and fishing mortality ranged between population extinction, quasi-extinction, to a slight reduction in population size and in some cases the population continuing to recover. The most pessimistic scenarios were when the initial population was lowest and post-release mortality in the shrimp trawl fishery was highest. Quasi-extinction for some scenarios was between 6.9 and 22.8 years. While some scenarios suggest that smalltooth sawfish still can recover despite the potential for shrimp trawl fishing mortality, key input variables for these optimistic scenarios is the initial population size and the true level of fishing mortality. This uncertainty highlights the importance of improving our understanding of sawfish life history, captures in fisheries and their associated post-release mortality.

The fate of intracoelomic acoustic transmitters in Atlantic salmon (Salmo salar) post-smolts and wider considerations for causal factors driving tag retention and mortality in fishes

Acoustic telemetry is a widely used method in assessing behavioural dynamics in fishes. Telemetry transmitters (tags) are often surgically implanted in the coelom of the animal with limited in situ testing and sometimes only assuming that they have minimal rates of post-release tag shedding and mortality. However, fish are capable of expelling tags and mortalities do occur following release, with the mechanism (s) underlying these effects not well-understood. The purpose of this research was to address causal factors underlying tag expulsion and tagging mortality in fishes. We conducted an empirical assessment of tag retention and post-surgical mortality rates in post-smolt Atlantic salmon (Salmo salar) fitted with dummy (non-transmitting) acoustic tags over a 92-day monitoring period. This was complimented with a meta-analysis of factors affecting tag retention and post-surgical mortality rates in the wider literature. Post-smolt salmon had high rates of tag expulsion (54.8%), impaired growth, and a foreign body response evident but exhibited low rates of mortality following tag implantation (≤ 5.1%). The meta-analysis showed that mortality was generally low across all studies (12.4%) and was largely unaffected by model cofactors. Tag retention rates were high among the studies investigated here (86.7%) and had a weak negative relationship with tag:body mass ratios. Our results suggest that while mortality is often low among tagging studies, including this one, caution must be exercised in assessing stationary tag location data as they may represent an expelled tag rather than a mortality event. Our results also indicate that tag dimensions are not nearly as important as the tag:body mass ratio.

When Prison Becomes the Devil’s Workshop: The Association Between Idleness and Post-Release Employment, Recidivism, and Mortality

The existing literature has yet to examine the system-wide effects of idleness and participation in prison-based work and programing on multiple post-release outcomes. Using a sample of more than 77,000 releases from Minnesota prisons between 2010 and 2021, we examined the relationship between participation in prison labor and programing on post-release employment, recidivism, and mortality. The findings suggest that how people spend their time in prison significantly affects their chances of finding a job, their likelihood of recidivism, and how long they live following release from prison. As involvement in work and/or programing increased, the people released from prison were more likely to find employment while also having a reduced risk for recidivism and mortality.

Postrelease mortality of spring Chinook Salmon from a mark‐selective recreational fishery in the Yakima River, Washington

AbstractObjectiveFishery managers often implement mark‐selective fishing regulations that provide harvest opportunity on abundant hatchery salmon populations while requiring release of at‐risk natural‐origin populations. However, implementing these decisions requires fisheries managers to account for postrelease mortality of any natural‐origin fish caught and released by anglers, which can be variable and is unknown for spring Chinook Salmon Oncorhynchus tshawytscha recreational fisheries in eastern Washington. Therefore, the objective of this study was to estimate and examine the factors affecting, the postrelease mortality of spring Chinook Salmon caught and released from an inland recreational mark–selective fishery in the Yakima River, Washington.MethodsWe conducted a 2‐year paired control and treatment radio‐telemetry study using 171 treatment fish caught and released during a recreational fishery and 194 control fish captured in a nearby fishway. Subjects were subsequently tracked throughout the summer, and postrelease mortality was estimated on September 1. Stepwise logistic regression was used to analyze potential explanatory variables recorded at the time of capture.ResultThe estimated postrelease mortality of these fish was 12% (95% CI = 2–23%) just prior to the onset of spawning. We also inferred using logistic regression that anatomical hook location explained most of the variation in mortality rates of angled fish.ConclusionOur estimate of postrelease mortality is similar to estimates derived in other studies for recreational freshwater Chinook Salmon fisheries as well as the current 10% rate used to manage Columbia River spring Chinook Salmon recreational fisheries.

Whole-lake acoustic telemetry to evaluate survival of stocked juvenile fish

Estimates of juvenile survival are critical for informing population dynamics and the ecology of fish, yet these demographic parameters are difficult to measure. Here, we demonstrate that advances in animal tracking technology provide opportunities to evaluate survival of juvenile tagged fish. We implemented a whole-lake telemetry array in conjunction with small acoustic tags (including tags < 1.0 g) to track the fate of stocked juvenile cisco (Coregonus artedi) as part of a native species restoration effort in the Finger Lakes region of New York, USA. We used time-to-event modeling to characterize the survival function of stocked fish, where we infer mortality as the cessation of tag detections. Survival estimates revealed distinct stages of juvenile cisco mortality including high immediate post-release mortality, followed by a period of elevated mortality during an acclimation period. By characterizing mortality over time, the whole-lake biotelemetry effort provided information useful for adapting stocking practices that may improve survival of stocked fish, and ultimately the success of the species reintroduction effort. The combination of acoustic technology and time-to-event modeling to inform fish survival may have wide applicability across waterbodies where receiver arrays can be deployed at scale and where basic assumptions about population closure can be satisfied.

Condition and postrelease mortality of angled Northern Pike temporarily retained on stringers

AbstractObjectiveAnglers typically use stringers to keep fish intended for harvest from spoiling or for high‐grading purposes (i.e., culling). However, relatively few studies have examined the effects of temporary stringer retention on the physical condition and postrelease mortality of fish. In this study, our objective was to investigate the lethal and sublethal effects of temporarily retaining Northern Pike Esox lucius on stringers.MethodsWe evaluated the blood physiology, reflex impairment, injury, and fate of 168 Northern Pike that were exposed for 2 h on one of five treatments: (1) cord stringer through the operculum, (2) cord stringer through the lower jaw, (3) metal stringer through the operculum, (4) metal stringer through the lower jaw, and (5) aerated tank control.ResultImmediately after retention, blood lactate concentrations of stringer treatments were on average 42% greater relative to controls. Fish from the stringer treatments exhibited injuries of varying severity, most of which (e.g., gill lesions, expanded puncture wounds, swelling) were still present on surviving fish 48 h later. Reflexes were impaired for all stringer fish, whereas control fish tended to have all reflexes intact. No fish died during the treatment period. The highest occurrence of mortality was within the first 8 h following retention for the cord–operculum (48%), metal–jaw (15%), and metal–operculum (19%) treatments. Stringers placed through the operculum had a higher mortality rate (37%) compared with stringers placed through the lower jaw (17%), regardless of stringer type. Overall, 27% of fish placed on stringers died and 68% of the remaining fish showed injuries related to stringers, while control fish showed low mortality (7%) and no meaningful injuries.ConclusionOur results suggest that holding fish on stringers causes stress and injury levels that can result in postrelease mortality. As such, fisheries managers should consider restricting the release of fish placed on stringers, and once placed on a stringer, fish should be regarded as part of the daily harvest limit for a given angler.

Socio-cultural relationship between recreational sea anglers and blue sharks (Prionace glauca) in the United Kingdom

The blue shark (Prionace glauca) is commonly caught by recreational anglers around the United Kingdom (UK) – part of a population (North Atlantic) which has sustained declines of > 50% over the last three generations (36 years). Therefore, mitigating any detrimental impacts recreational fisheries might have on this species is crucial. This requires understanding anglers’ perceptions and behaviours, to co-design appropriate management measures. Here, we explore the socio-cultural relationship between anglers and blue sharks in the UK through structured surveys. A total of seven business operators and 44 recreational anglers responded throughout Aug-Nov 2021. Respondents primarily comprised of over-fifty, educated and wealthy male anglers. A positive relationship was identified: 100% of anglers have respect for sharks; 80% (n = 42) would like their fishing to inform research. We also found that socio-demographic variables correlate with certain perceptions, e.g., education level and political leanings were associated with the level of agreement to the statement “sharks are there for my enjoyment to catch” and “I want to catch the biggest shark possible”, respectively. Operators follow best fishing practices to minimise stress to sharks and 100% of operators wanted to contribute to research. Currently 43% (n = 3) submit catch data and one operator tags sharks. This willingness to contribute to research could improve our understanding of blue shark population structure, habitat use, and post-release mortality rates associated with recreational angling. This will not only help sustain shark stocks but also engage anglers in understanding the threats to sharks and benefit recreational fisheries that rely on stable shark populations.

Effects of climate change and variability on large pelagic fish in the Northwest Atlantic Ocean: implications for improving climate resilient management for pelagic longline fisheries

Climate change influences marine environmental conditions and is projected to increase future environmental variability. In the North Atlantic, such changes will affect the behavior and spatiotemporal distributions of large pelagic fish species (i.e., tunas, billfishes, and sharks). Generally, studies on these species have focused on specific climate-induced changes in abiotic factors separately (e.g., water temperature) and on the projection of shifts in species abundance and distribution based on these changes. In this review, we consider the latest research on spatiotemporal effects of climate-induced environmental changes to HMS’ life history, ecology, physiology, distribution, and habitat selection, and describe how the complex interplay between climate-induced changes in biotic and abiotic factors, including fishing, drives changes in species productivity and distribution in the Northwest Atlantic. This information is used to provide a baseline for investigating implications for management of pelagic longline fisheries and to identify knowledge gaps in this region. Warmer, less oxygenated waters may result in higher post-release mortality in bycatch species. Changes in climate variability will likely continue to alter the dynamics of oceanographic processes regulating species behavior and distribution, as well as fishery dynamics, creating challenges for fishery management. Stock assessments need to account for climate-induced changes in species abundance through the integration of species-specific responses to climate variability. Climate-induced changes will likely result in misalignment between current spatial and temporal management measures and the spatiotemporal distribution of these species. Finally, changes in species interactions with fisheries will require focused research to develop best practices for adaptive fisheries management and species recovery.

A novel automatic release cage increases survival of Atlantic salmon (Salmo salar) smolts released at night.

Trap-and-transport of migratory fish is commonly used to bypass in-river obstructions. On the River Conon in Scotland, Atlantic salmon (Salmo salar) smolts are transported around two hydropower facilities. Smolt release occurs during daylight, when predation rates can be high. A novel automatic release cage (ARC) was designed to release smolts at night. Smolts were fitted with acoustic tags (n = 99) to compare survival. High post-release mortality was identified in the day-release group, with night-release survival >40% higher. ARCs can provide fishery managers with a cost-effective and reliable method of improving smolt survival.

Using intervention analysis to evaluate the trends in release rates of recreational fisheries following extensive management changes

Changes to management of a fisheries resource are often required to ensure ongoing sustainability. However, such changes can sometimes lead to unintended effects such as increased release rates and associated post-release mortality. These effects may be highly variable between species and areas. Recreational fishing management changes were introduced on the west coast of Australia in 2009/10 to recover stocks of demersal scalefish. Key changes included reducing mixed species bag limits across management zones and increasing the minimum size limit for one species in some management zones. The restrictive catch limits resulted in increased release rates of key demersal species. However, whether such increases are significant and sustained over time, and thus of management concern, have not been evaluated. We carried out intervention time series analysis to evaluate the impact of management changes on release rates of four key demersal species for the recreational sector in metropolitan and regional management zones covering ∼8° latitude using an 18-year time series of charter recreational fishery data from July 2002 to January 2020. We observed varying responses in release rates by species and zones, the most common of which were a step increase, a ramp and a temporary increase that decayed. These responses may be related to targeted management changes which influenced fisher behaviour, perceived recreational value of some species and recruitment variation. Our study demonstrates that intervention analysis, which has seen limited use in this context, can assist in evaluating the impact of management changes on different species for recreational fisheries.