Kevin D. Friedland

Stock identification and its role in stock assessment and fisheries management: an overview

Abstract A symposium on “Stock Identification – its Role in Stock Assessment and Fisheries Management” was held as part of the 128th annual meeting of the American Fisheries Society (AFS), Hartford, Connecticut, USA, 23–27 August 1998, to summarize the current state of knowledge of stock identification issues, problems and methodologies, as well as to identify future directions for stock identification research. With today’s, growing emphasis on stock assessment, this symposium was a timely reminder of the need to identify fish stocks accurately, and the implications of stock identification for fisheries management. The symposium was structured into four general themes: (1) the stock concept; (2) genetic variation; (3) phenotypic variation; and (4) fisheries management. We review the presentations given in each theme session, which form the basis of the proceedings presented in this issue, as well as providing an overview of current issues and directions in stock identification research. We hope that the overall proceedings constitute a text helpful in these directions, useful in the classroom, laboratory, and field.

The utility of image processing techniques for morphometric analysis and stock identification

Abstract The development of image analysis systems has facilitated progress and diversification of morphometric methods and expands the potential for using morphometry as a tool for stock identification. Identifying intraspecific groups with different life histories according to shape variation has become more powerful, based on a review of published studies and our experiences with American lobster and Atlantic salmon. Traditional multivariate morphometrics, accounting for variation in size and shape, have successfully discriminated many fish stocks. However, traditional methods have been enhanced by image processing techniques, through better data collection, more effective descriptions of shape, and new analytical tools. Properly calibrated coordinates of morphometric locations, or ‘landmarks’, are generally more efficient and precise than manual distance measurements. ‘Truss networks’ of distances between landmark coordinates provide more comprehensive coverage of form for greater discriminating power. Image analysis systems also allow more advanced ‘geometric morphometrics’, which include outline methods and landmark methods. Unfortunately, few stock identification studies have applied outline methods, and landmark methods have not been used to discriminate fishery stocks. It appears that advanced geometric methods have not been commonly applied in fishery science, because ontogenetic interpretations are difficult.

The emerging role of climate in post-smolt growth of Atlantic salmon

Friedland, K. D., Chaput, G., and MacLean, J. C. 2005. The emerging role of climate in post-smolt growth of Atlantic salmon. e ICES Journal of Marine Science, 62: 1338e1349. Though it is well established that mortality during the post-smolt year is critical in shaping recruitment patterns in Atlantic salmon (Salmo salar L.), the controlling mechanism for North Atlantic stocks remains elusive. The emerging paradigm is based on relationships between survival and ocean thermal conditions during the early marine phase. The survival of post-smolts from both Europe and North America has been correlated to sea surface temperature conditions during their first month at sea. In addition, data for European fish support the hypothesis that growth mediates survival during that time. Thus, the working model for a salmon recruitment mechanism is analogous to those proposed for other fish species. We present growth data for two stocks, the Girnock Burn, which is a tributary to the River Dee, Scotland, and the Margaree River, Canada. Circuli spacing data for Girnock Burn fish suggest post-smolt growth is negatively correlated with temperature in the migration corridors during the first months at sea, while post-smolt growth of Margaree fish appears to be positively correlated with temperature. Growth is either patterned by a physiological response to an optimal temperature, or is co-varying with some ecosystem effect on growth, and the growth response might affect mortality and maturation of the stocks. Published by Elsevier Ltd on behalf of International Council for the Exploration of the Sea.

Ocean thermal conditions in the post-smolt nursery of North American Atlantic salmon

The effect of climate on the post-smolt survival of North American Atlantic salmon is obscure owing to the difficulty in interpreting the only relationships thus far observed between the abundance of these stocks and climate, which focuses on winter conditions. Placing significance on winter post-smolt survival is contrary to conventional thinking that the spring period is more important, because that is when the post-smolts migrate to sea and transition to ocean life takes place. The pre-fishery abundance for North American stocks was compared to thermal conditions in potential post-smolt nursery areas during the period 1982-1999. Pre-fishery abundance was modeled as a reconstruction of one-sea-winter (1SW) and two-sea-winter (2SW) age salmon populations. Cohort abundance was compared to mean temperature and thermal habitat (sea surface area within a given temperature range) in five index areas. Stock size was negatively correlated with mean sea surface temperature during June. Correlations were comparatively stronger between stock abundance and thermal habitat, further asserting that June conditions - the first month at sea for most stocks in the region - may be pivotal to survival. These correlations suggest that post-smolt survival is negatively affected by the early arrival of warm ocean conditions in the nursery area. Hypotheses related to post-smolt migration, predation, and the availability of suitable prey are discussed.

A history of identification to continent of origin of Atlantic salmon (Salmo salar L.) at west Greenland, 1969–1997

Atlantic salmon caught in the commercial fishery at west Greenland have routinely been identified to continent of origin, viz., North American or European, since 1969, using scale pattern recognition techniques. Although specific details have varied over the 29-year period, the technique generally has remained the same. Discriminant analysis of scale samples collected in the commercial fishery (mixed samples) and a known origin database (training samples) collected in homewaters are used to identify the continental origin of individual fish. The proportions of North American salmon in the catch samples have ranged from a low of 34% in 1971 to a high of 75% in 1990. Comparisons of the North American proportions showed no consistent spatial trends, however, differences were noted in proportions with latitude along the west Greenland coast. The proportions of continent of origin, although varying annually, have generally shown an increasing proportion of North American salmon in recent years. Biological characteristics of individual salmon identified to continent of origin have been used in models to provide catch advice to managers for the west Greenland salmon fishery and to define the impacts of the fishery on salmon stocks.

Atlantic Sturgeon Marine Distribution and Habitat Use along the Northeastern Coast of the United States

Abstract Though the distribution of Atlantic sturgeon Acipenser oxyrinchus is relatively well known in freshwater and estuarine habitats in the northern portion of their range, their distribution in marine habitats is poorly understood. Sturgeon migrate into marine waters to forage between spawning events and probably maintain gene flow between river populations by entering nonnatal river systems to spawn. While at sea, they are captured in commercial fishing gears. We investigated data collected by onboard fishery observers to determine the occurrence and habitat preference of Atlantic sturgeon off the northeastern coast of the United States. Sturgeon distributions were based on monitored fishing trips over the period 1989–2000 and referenced to local bathymetry and sediment data. The results show that peak sturgeon captures along the coast were approximately bracketed by isobaths ranging from 10 to 50 m. Sturgeon were present more frequently on gravel and sand sediment types and were associated with spe...

Temperature sensor evaluation of opossum winter activity

Abstract To effectively monitor winter foraging activity by the cryptic, non-site-faithful Virginia opossum (Didelphis virginiana), we tested the use of small data-logging temperature sensors (iButton Thermachrons®, Maxim/Dallas SemiConductors, Dallas, Tex.) attached to a standard radiocollar on 3 opossums over the winter of 2000–2001. Two replicate sensors were required to clearly show time periods with cooler temperatures, an indication that the animal was outside the den. These foraging bouts were consistent with the available radiotelemetry data. Daily duration of foraging showed a strong negative relationship with ambient temperature, quantitatively documenting for the first time a phenomenon previously known only anecdotally. The iButton Thermachron seems to be an effective, low-cost, and low-effort technology for monitoring foraging activities of any animal that rests and forages in different temperature environments.

Stock Identification Methods

Publisher Summary Stock identification is an interdisciplinary field that involves the recognition of self-sustaining components within natural populations and is a central theme in fisheries science and management. The obvious role of stock identification is as a prerequisite for the tasks of stock assessment and population dynamics, because most population models assume that the group of individuals has homogeneous vital rates (e.g., growth, maturity, and mortality) and a closed life cycle in which young fish in the group were produced by previous generations in the same group. Because stock structure and delineation are uncertain, the reliability of stock assessments, and therefore the effectiveness of fishery management, is severely limited for many fishery resources. There are also roles for stock identification in fishery science that may be equally important but less obvious. Whether the research concerns general life history, growth, physiology, or diet, the population of inference and its stock components should be identified. Therefore, stock identification can be viewed as a prerequisite for any fishery analysisPublisher Summary Stock identification is an interdisciplinary field that involves the recognition of self-sustaining components within natural populations and is a central theme in fisheries science and management. The obvious role of stock identification is as a prerequisite for the tasks of stock assessment and population dynamics, because most population models assume that the group of individuals has homogeneous vital rates (e.g., growth, maturity, and mortality) and a closed life cycle in which young fish in the group were produced by previous generations in the same group. Because stock structure and delineation are uncertain, the reliability of stock assessments, and therefore the effectiveness of fishery management, is severely limited for many fishery resources. There are also roles for stock identification in fishery science that may be equally important but less obvious. Whether the research concerns general life history, growth, physiology, or diet, the population of inference and its stock components should be identified. Therefore, stock identification can be viewed as a prerequisite for any fishery analysis

Stock Identification Methods: An Overview

Publisher Summary Stock identification is an interdisciplinary field that involves the recognition of self-sustaining components within natural populations and is a central theme in fisheries science and management. The obvious role of stock identification is as a prerequisite for the tasks of stock assessment and population dynamics, because most population models assume that the group of individuals has homogeneous vital rates (e.g., growth, maturity, and mortality) and a closed life cycle in which young fish in the group were produced by previous generations in the same group. Because stock structure and delineation are uncertain, the reliability of stock assessments, and therefore the effectiveness of fishery management, is severely limited for many fishery resources. There are also roles for stock identification in fishery science that may be equally important but less obvious. Whether the research concerns general life history, growth, physiology, or diet, the population of inference and its stock components should be identified. Therefore, stock identification can be viewed as a prerequisite for any fishery analysisPublisher Summary Stock identification is an interdisciplinary field that involves the recognition of self-sustaining components within natural populations and is a central theme in fisheries science and management. The obvious role of stock identification is as a prerequisite for the tasks of stock assessment and population dynamics, because most population models assume that the group of individuals has homogeneous vital rates (e.g., growth, maturity, and mortality) and a closed life cycle in which young fish in the group were produced by previous generations in the same group. Because stock structure and delineation are uncertain, the reliability of stock assessments, and therefore the effectiveness of fishery management, is severely limited for many fishery resources. There are also roles for stock identification in fishery science that may be equally important but less obvious. Whether the research concerns general life history, growth, physiology, or diet, the population of inference and its stock components should be identified. Therefore, stock identification can be viewed as a prerequisite for any fishery analysis

Chapter 8 – Morphometric Outlines

Publisher Summary The study of shape variation has advanced from measuring simple linear distances to deriving geometric variables. The shift from traditional morphometrics to more complex geometric functions was facilitated by the development of image processing tools. Recently developed geometric approaches to morphometric analysis are generally categorized as either “landmark methods” or “outline methods.” Geometric outline methods quantify boundary shapes so that patterns of shape variation within and among groups can be evaluated. Patterns of variation in the shape of fish scales and otoliths as well as mollusc valves have been used to identify phenotypic stocks. Prior to the development of outline methods, researchers noted that otolith shape varied among stocks. However, efficient classification of fish to the correct stock requires quantification of shape and its variation. The most common outline method involves fitting a Fourier series to the point coordinates along the perimeter of a morphometric feature. Fourier coefficients are commonly used as multivariate observations for discriminant analysis, and several studies have successfully used Fourier transforms of scale or otolith shape for group discrimination of finfish stocks.