John Walter

National Oceanic and Atmospheric Administration | NOAA · Southeast Fisheries Science Center

Global climate change threatens the assumption of stationarity inherent in many fisheries management decisions. This heightens the importance of developing management strategies that are robust to future uncertainty. Management strategy evaluation (MSE) is a framework in which management procedures (MPs) can be developed and tested using closed-loo...

Fishers in the United States pelagic longline fishery are required to self-report all fishing interactions (captures) on a per-set basis to the National Oceanic and Atmospheric Administration (NOAA) to quantify catch, increase conservation efforts, and allow for an accounting of international quota-managed species. Additionally, trained fisheries o...

The commercially important Atlantic bluefin tuna ( Thunnus thynnus ), a large migratory fish, has experienced notable recovery aided by accurate resource assessment and effective fisheries management efforts. Traditionally, this species has been perceived as consisting of eastern and western populations, spawning respectively in the Mediterranean S...

Strategic plan for the use of management strategy evaluation at the NOAA Fisheries Southeast Fisheries Science Center

Natural geochemical markers in the otolith of yellowfin tuna (Thunnus albacares) were used to establish nursery-specific signatures for investigating the origin of fish captured in the western Atlantic Ocean (WAO). Two classes of chemical markers (trace elements, stable isotopes) were used to first establish nursery-specific signatures of age-0 yel...

Climate change impacts on fish stocks may include changes in ecological interactions, spatial redistribution, and changes in productivity. Predicting precisely what will happen to fish stocks with any future climate changes is challenging. Climate change science could be used in the assessment process a) using indicator-based approaches to provide...

The commercially important Atlantic bluefin tuna (Thunnus thynnus), a large migratory fish, has experienced notable recovery aided by accurate resource assessment and effective fisheries management efforts. Traditionally, this species has been perceived as consisting of eastern and western populations, spawning respectively in the Mediterranean Sea...

The basis of natural resource management is decision making under uncertainty while balancing competing objectives. Within fisheries management , a process described as management strategy evaluation (MSE) is becoming increasingly requested globally to develop and test management procedures. In a fisheries or other natural resource context, a manag...

Globally, tunas are among the most valuable fish stocks, but are also inherently difficult to monitor and assess. Samples of larvae of Western Atlantic bluefin tuna Thunnus thynnus (Linnaeus, 1758) from standardized annual surveys in the northern Gulf of Mexico provide a potential source of “offspring” for close-kin mark-recapture (CKMR) estimates...

Atlantic bluefin tuna (Thunnus thynnus) are large, highly migratory fish that support important fisheries. Oceanic conditions influence Atlantic bluefin tuna distribution and it has been hypothesized that stock distributions have shifted in recent years. Distributional shifts can affect regional availability and fleet catchability, introducing a po...

Marine artificial structures provide important ecosystem benefits, but the extent to which commercially valuable reef fish species and their associated fisheries utilize artificial structures is still undetermined. However, the increasing implementation of onboard Vessel Monitoring Systems (VMS) now enables precise identification of catch and effor...

This document presents results from across the four remaining CMPs for the BFT MSE: BR, TC, LW and FO. The document illustrates tradeoffs, key decision points for Panel 2, and the essential components of each CMP. CMP rank ordering is largely conserved across the different variants of 2 versus 3-year TAC setting interval, PGK60% or PGK70%. For the...

Age, growth, and mortality were estimated for Yellowfin Tuna Thunnus albacares from the U.S. Gulf of Mexico and western Atlantic Ocean. During 2004–2017, 3,443 Yellowfin Tuna were sampled, primarily from recreational landings off the coast of Louisiana (90%). Based on reading otoliths, ages ranged from 1 to 18 years, with younger fish (<4 years) re...

Atlantic bluefin tuna (Thunnus thynnus) are a large, highly migratory fish distributed throughout the North Atlantic Ocean and adjacent seas currently managed as two discrete stocks: western and eastern. Both stocks forage in the North Atlantic, and a high degree of intermixing occurs, which combined with limited single-stock survey data makes it d...

Impacts of Karenia brevis red tide blooms have been an increasing cause of concern for fisheries management in the Gulf of Mexico (Gulf). The 2019 Gulf red grouper (Epinephelus morio) stock assessment was confronted with the challenges of quantifying and parameterizing red tides during both historical and projection time periods. Red tide mortality...

The ecosystem‐based fisheries management (EBFM) framework has a solid theoretical justification and has been embraced in principle by many regions; yet, systematic implementation remains a challenge. In regions with strong governance, single‐species stock assessment and management has been successful in ending overfishing and maintaining stocks nea...

We evaluated the effects of the alternative recruitment assumptions in the Atlantic bluefin tuna MSE on the performance of the PW candidate management procedure. We deterministically tuned the CMP to the 30-year biomass ratio (Br30) estimates to each individual recruitment scenario separately (R1, R2, R3), then all recruitment scenarios (RA), and f...

The three main robustness tests, senescence, growth curve for eastern stock, "Brazilian" catches, had already been coded in July 2020 (with 4 Operating Models (OMs) each), but the "Brazilian" catches test needed to be redone. Robustness tests on time-varying mixing and persistent change in mixing have now also been coded (with 2 OMs each) and will...

Many fisheries and marine science organizations are working to determine how to meet their missions in the midst of the COVID-19 outbreak. As such, it seems prudent to exchange ideas, share knowledge, and initiate a discussion among us. As the scientific leadership team for NOAA Fisheries, we wanted to offer some perspectives. Others are also evalu...

This review documents the current state of knowledge and gaps therein, as determined through a survey of published research on relevant topics, regarding the potential impacts of offshore oil production platforms (OPP) on the biology of highly migratory fish species (HMS) which include tunas, swordfish, billfishes, and oceanic sharks. There is a li...

Recreational fishers discard millions of red snapper (Lutjanus campechanus) annually in the northern Gulf of Mexico (nGOM), resulting in significant foregone yield. We conducted simulation modeling to evaluate the potential for hook-size regulations to improve efficiency in the recreational red snapper fishery. First, we imposed a suite of candidat...

Atlantic Bluefin Tuna Stock Assessment

Bayesian State-Space Surplus Production Models were fitted to yellowfin tuna catch and standardized catch-per-unit-effort (CPUE) data using the open-source stock assessment tool JABBA. Here, we present results from six scenarios (base case model and S1-S5).These scenarios corresponded to combinations of different CPUEs associated with three alterna...

This paper presents a multivariate lognormal (MVLN) Monte-Carlo approach to produce Kobe phase plots and Kobe II projection matrices for range of fixed catch scenarios from the 2018 Indian Ocean yellowfin tuna reference grid of Stock Synthesis models. First, we present Kobe-phase plots for the current stock status that compare within-model uncertai...

Management strategy evaluation (MSE) is an increasingly popular tool for developing, testing, and implementing fisheries management regimes, oftentimes utilizing participatory modeling. This special issue, “Under pressure: addressing fisheries challenges with Management Strategy Evaluation”, includes eleven articles highlighting cutting edge MSE ap...

Effective sustainable management of marine fisheries requires that assessed management units (that is, fish stocks) correspond to biological populations. This issue has long been discussed in the context of Atlantic bluefin tuna (ABFT, Thunnus thynnus) management, which currently considers two unmixed stocks but does not take into account how indiv...

Age-length key (ALK) methods generally perform well when length samples and age samples are representative of the underlying population. It is unclear how well these methods perform when lengths are representative but age samples are sparse (i.e. age samples are small or missing in many years, and some length groups do not have any age observations...

In the United States, implementation of strong legislative mandates and investments in scientific programmes have supported sustainable fisheries management for seafood production, marine ecosystems, and maritime communities and economies. Changing climate and ocean conditions present new and growing challenges that affect the ability to manage fis...

The timing and extent of international crossings by billfishes, tunas, and sharks in the Cuba-Mexico-United States (U.S.) triangle was investigated using electronic tagging data from eight species that resulted in >22,000 tracking days. Transnational movements of these highly mobile marine predators were pronounced with varying levels of bi- or tri...

Many stock assessments heavily rely on indices of relative abundance derived from fisheries-dependent catch-per-unit-effort (CPUE) data. Therefore, it is critical to evaluate different CPUE standardization methods under varying scenarios of data generating processes. Here, we evaluated nine CPUE standardization methods offering contrasting treatmen...

Bluefin tuna (Thunnus thynnus) of the western Atlantic Ocean are often incidentally caught in the pelagic longline fishery that targets swordfish (Xiphias gladius) and yellowfin tuna (Thunnus alba-cares) in the Gulf of Mexico. Data on at-vessel and postrelease mortality are lacking. Using the database of the NOAA Southeast Fisheries Science Center'...

Management strategy evaluation (MSE) is a simulation-based approach to examine the efficacy of management options in achieving fishery-, ecosystem-, and socioeconomic-related objectives while integrating over system uncertainties. As a form of structured decision analysis, MSE is amenable to stakeholder involvement, which can reduce implementation...

Specifying annual catch limits for artisanal fisheries, low economic value stocks, or bycatch species is problematic due to data limitations. Many empirical management procedures (MPs) have been developed that provide catch advice based on achieving a stable catch or a historical target (i.e., instead of maximum sustainable yield). However, a thoro...

Environmental variability changes the distribution, migratory patterns, and susceptibility to various fishing gears for highly migratory marine fish. These changes become especially problematic when they affect the indices of abundance (such as those based on catch-per-unit-effort: CPUE) used to assess the status of fish stocks. The use of simulate...

Updating indices of red tide severity for incorporation into stock assessments for the shallow-water grouper complex in the Gulf of Mexico. SEDAR61-WP-07. SEDAR, North Charleston, SC. 12 pp.

Abundance-at-age and mortality estimates of western Atlantic bluefin tuna were compared between Stock Synthesis and virtual population analysis. Estimates of mean recruitment (age 1 abundance) used for projecting stock biomass did not vary greatly between models; however, the size of individual age classes varied with Stock Synthesis (SS) estimatin...

Estimates of catch-at-age are presented for the western and eastern stocks of Atlantic bluefin tuna using a combined forward-inverse age-length key for the period 1974 to 2015 and 1968 to 2015, respectively. Results indicated signals of strong and weak cohorts with the 2002 year class standing out as a relatively strong cohort. Convergence issues c...

A series of estimates of the total mortality rate (Z) can be obtained by using the Beverton–Holt nonequilibrium-based approach of Gedamke and Hoenig (2006) on observations of population mean length over time (ML model). In contrast, only relative mortality rates (not absolute values) can be obtained from a time series of catch rates. We derived the...

Environment–recruitment relationships can be difficult to delineate with parametric statistical models and can be prone to misidentification. We use non-parametric time-series modeling which makes no assumptions about functional relationships between variables, to reveal environmental influences on early life stages of bluefin tuna and demonstrate...

The article examines factors related to the decline and rebuilding of billfish stocks in the Atlantic and Indian oceans. Longline effort has declined over the last 10–15 years in both oceans. This decline in fishing pressure has led to the recovery of some stocks, but some species that are caught incidentally in industrial longline fisheries remain...

Bycatch in pelagic longline fisheries is of substantial international concern, and the mitigation of bycatch in the Gulf of Mexico has been considered as an option to help restore lost biomass following the 2010 Deepwater Horizonoil spill. The most effective bycatch mitigation measures operate upon a differential response between target and bycatch...

Mapping the spatial distributions of fish populations is an integral component of ecosystem-based fisheries management (EBFM). Particularly for red grouper (Epinephelus morio) and gag grouper (“gag”; Mycteroperca microlepis), two economically important species, the lack of mapping due to data limitations (i.e., inconsistent capture in research surv...

In 2011, an intensive, multiple-gear, fishery-independent survey was carried out in the northern Gulf of Mexico (GOM) to collect comprehensive age and length information on Red Snapper Lutjanus campechanus. Based on this synoptic survey, we produced a spatial map of Red Snapper relative abundance that integrates both gear selectivity effects and on...

Catastrophic disturbances to marine environments, such as the Deepwater Horizon oil spill in the northern Gulf of Mexico (GoM), emphasize the need to approach fisheries management and restoration from an ecosystem perspective. To evaluate the ecosystem dynamics within the GoM, we developed a mass-balanced Ecopath model (“nGoM Ecopath”) which integr...

A stock assessment was conducted for yellowfin tuna in 2016, applying three age-structured models and a non-equilibrium surplus production model to data through 2014. Models used to develop management advice considered two primary sources of scientific uncertainty, the use of index clusters that reflect two disparate hypotheses regarding trends in...

This document represents a meeting report of a small working group that convened to evaluate the feasibility of combining set by set data from the Japan, Canada, Mexico and United States pelagic longline fishing fleets to obtain a CPUE index for Western Atlantic Bluefin tuna, while maintaining data confidentiality. The group was successful in combi...

Conflicting trends in indices of abundance for North Atlantic swordfish starting in the mid-to late 1990 s, in the form of fleet specific catch-per-unit-effort (CPUE), suggest the possibility of a spatial shift in abundance to follow areas of preferred temperature. The observed changes in the direction of the CPUEs correspond with changes in trends...

The discovery of 67 bluefin tuna larvae in waters off the northeast US continental shelf is certainly of considerable scientific interest, but the paper in PNAS by Richardson et al. (1) makes several broad assertions that go beyond what the data support. The authors extrapolate differences in larval catch rates to conclude that the majority of spaw...

[This corrects the article DOI: 10.1371/journal.pone.0141478.].

The Gulf of Mexico (GOM) is the primary spawningground for western Atlantic bluefin tuna(Thunnusthynnus). In this work, information reported by previ-ous studies about the preferred environmental condi-tions for the occurrence of bluefin tuna larvae in theGOM is integrated into a dimensionless index, theBFT_Index. This index is used to evaluate the...

The Gulf Menhaden Brevoortia patronus is frequently cited as playing a predominant role in the trophic structure and function of the northern Gulf of Mexico (GOM) marine ecosystem, yet much work remains in quantifying its ecological importance. We performed a meta‐analysis of diet studies to quantify the trophic role of Gulf Menhaden within this ec...

Recent collaborative efforts in standardizing swordfish longline catch and effort information across U.S. and Canadian fleets allowed for hypothesis testing of stock distribution shift effects on fleet catchabilities. Scientists and managers agreed that a similar effort is worth pursuing for highly migratory stocks in which a changing oceanic envir...

The compiled data for this study represents the first Atlantic and Mediterranean-wide effort to pool all available biometric data for Atlantic bluefin tuna (Thunnus thynnus) with the collaboration of many countries and scientific groups. Biometric relationships were based on an extensive sampling (over 140,000 fish sampled), covering most of the fi...

We develop and test spatial population dynamics models that estimate age-dependent offshore movement of fish populations from spatial fishery data. Spatially aggregated population dynamics models produced biased estimates of maximum sustainable yield (MSY) reference points when spatial dynamics were simulated. Spatial population dynamics models pro...

Geostatistical prediction can address two difficult issues in interpreting fishery‐dependent catch per unit effort (CPUE): the lack of a sampling design and the need to fill spatial gaps. In this paper we demonstrate the spatial weighting properties of geostatistics for treating data collected without a sampling design or with a selection bias, two...

Fishery‐dependent catch per unit effort (CPUE) comprises critical input for many stock assessments. Construction of CPUE indices usually employs some method of data standardization. However, conventional methods based on linear models do not effectively deal with the fact that samples are collected with a selection bias or with the problem of filli...

A large Integrated Ecosystem Assessment (IEA) program has been initiated in the Gulf of Mexico (GOM). One goal of the GOM IEA program is to incorporate ecosystem products into single-species stock assessments. In 2013-2014, ecosystem considerations were introduced in the Stock Synthesis (SS) assessment model of GOM gag grouper (Mycteroperca microle...