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Reaction norm analysis of fisheries-induced adaptive change and the case of the Northeast Arctic cod
2002
We present a probabilistic concept of reaction norms for age and size at maturation, and outline methods that can be used for their estimation in typical fisheries data. Such estimations are critical for calibrating size-and age-structured population models, for understanding phenotypic plasticity and life-history changes in variable environments, and for assessing genetic changes in the presence of phenotypic plasticity. We apply the method of reaction norm estimation to a set of measurements on Northeast Arctic cod collected between 1932 and 1998. This cod stock has shown a drastic reduction in age at maturation. In the 1930's, age at maturation was typically around 10-11 years, whereas nowadays seven years is more usual. This change has been attributed both to fisheries-induced genetic selection for earlier maturation, and to a compensatory response caused by faster individual growth rate. However, previous analyses have been unable to disentangle these hypotheses. Our analysis, based on estimation of maturation reaction norms, shows that both increase in growth rate and change in age-and size-specific tendency to mature have contributed to the observed trend towards earlier maturation. The latter component probably represents a fisheries-induced adaptive genetic change.
Changes in distribution of Greenland halibut in a varying environment
ICES Journal of Marine Science, 2012
Morgan, M. J., Garabana, D., Rideout, R. M., Román, E., Pérez-Rodriguez, A. and Saborido-Rey, F. 2013. Changes in distribution of Greenland halibut in a varying environment. – ICES Journal of Marine Science, 70: 352–361. Fish are expected to respond to changing oceanographic temperature by altering their distribution. Off the coast of Newfoundland, Canada, there have been major changes in oceanographic temperature over the last several decades, with both record cold and record warm years being observed. Greenland halibut is an important flatfish species in the area, and is distributed in deep waters over a very wide geographic range. Thus, it might be buffered from temperature change in the overall area by reduced temperature variation at depth, and the diverse temperature conditions over its wide range. We examined intrapopulation variation in temperature and depth distribution, and the biological changes in relation to changes in available temperature. On the Flemish Cap, variatio...
An Extended Survivors Analysis (XSA) of the Greenland Halibut in NAFO SA 0+1
2000
An assessment of the Greenland halibut in NAFO Divisions 0+1 was carried out using Extended Survivors Analysis (XSA). Although the assessment results are considered to be provisional due to problems with the catch at age data and the short time series, the assessment is considered to reflect the dynamics of the stock. The results indicate that the stock increased during
ICES Journal of Marine Science, 2014
Since the late 1980s, a deep-sea fishery for Greenland halibut (Reinhardtius hippoglossoides) has been developing gradually in West Greenland. Deep-sea fish species are generally long-lived and characterized by late age of maturity, low fecundity, and slow growth, features that probably cause low resilience following overexploitation. In order to evaluate whether populations of nine potential bycatch species are negatively affected by the commercial fishery for Greenland halibut, scientific data from bottom-trawl surveys conducted in the same area and period as the commercial fishery were analysed. During the period 1988 -2011, population abundance and size composition changed as catch and effort in the Greenland halibut fishery increased. Two species showed a significant decrease in abundance, and four populations showed a significant reduction in mean weight of individuals (p , 0.05). Correlation analyses show that most of the observed trends in abundance are probably not related to increasing fishing effort for Greenland halibut. The analysis did, however, show that most of the observed decreases in mean weight were significantly correlated with fishing effort during the 24-year period.
Journal of Northwest Atlantic Fishery Science, 2003
The variation in population structure of Greenland halibut (Reinhardtius hippoglossoides Walbaum) in the Northeast Arctic is analysed using data from three different surveys using trawl, longline and gillnet gears, in the slope area of the western Barents Sea in the period 19922000. The design of the longline and gillnet survey had limitations in that they were set to simulate the commercial fisheries, but the vessels were forced to cover the most important part of the slope area. Greenland halibut was the dominant species both in numbers and weight and was usually caught in the range of 515 years old, but the catch was dominated by ages 612. The data showed differences in sex composition and age composition both by area and by depth, and catches from trawl showed the most evident pattern. Greenland halibut caught by gillnet were larger and older than fish caught by trawl and the results from longline were in between. In most of the age groups, males were significantly smaller than females and this general trend was shown for all gears. Males also dominated the younger age groups in all gears and Greenland halibut older than 10 years were virtually all females. Fish from the earliest cohorts in the years investigated were generally smaller than fish from later ones.
Fisheries Research, 2001
A joint Norwegian±Greenland longline survey was conducted at East Greenland in August 1997, using different hook and bait types. Most Norwegian longliners use hooks of the type EZ 12/0. This hook was compared to three versions of a new circle 14/0 hook. A total catch of 2899 Greenland halibut from 45,760 hooks baited with squid were used in the hook selectivity analyses. In average, CPUE was 281 kg/1000 hook for the EZ hook. CPUE for the circular hook was 36% higher making an overall signi®cant difference in CPUE between the EZ hook and the circle hooks. On 6630 hooks squid and grenadier were used alternately. The CPUE of Greenland halibut was 25% higher for grenadier bait. The grenadier bait resulted in a reduction in bycatch compared to the squid bait (1.1 and 20.7% by numbers, respectively). Catches by EZ 12/0 hook and one of the circle 14/0 hooks were compared in order to examine size selectivity. Using the SELECT approach, expected proportions were ®tted to the observed proportions for ®ve different models of selectivity. All models resulted in almost identical ®ts. The absence of non-selective data requires the choice of selectivity curve to be based on knowledge about the capture process. Since the selectivity curves cannot be determined unambiguously in this study, none of the estimated curves are preferred for the other.
Bulletin of Marine Science, 2016
In data-limited fisheries, making informed management decisions based on scientific advice is challenging. Here, we evaluate a multi-indicator adaptive management framework (AMF) that allows dynamic responses to changing environmental, socioeconomic, and fishing conditions. Using stakeholder-defined goals as a foundation for specifying performance metrics, we employ management strategy evaluation (MSE) to explore the performance of the AMF relative to prescriptive alternatives that are sometimes used in data-limited situations. We conduct simulations involving the two most economicallyimportant fisheries in Belize, spiny lobster, Panulirus argus (Latreille, 1804), and queen conch, Strombus gigas (Linnaeus, 1758). Spiny lobster fishery simulations demonstrate that when relatively stable catches have historically persisted, an AMF can help to ensure that stable catches continue to persist into the foreseeable future when faced with factors such as increased entry to the fishery or environmentallyinduced recruitment fluctuations. The queen conch fishery simulations demonstrate that optimizing economic performance is complicated without stock status indicators and depends greatly upon the current, yet typically unknown, state of the resource. Since our indicator-based approach could not provide direct information about resource status in relation to management reference points such as maximum sustainable yield, economic objectives could not be achieved. Nevertheless, implementing the AMF served as a beneficial control against stock collapse and could function well as an interim fishery policy during which sufficient fishery data could be collected to inform population modeling and quantitative stock assessment.