This is what I've had on my computer.
Research:
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FISHERIES IN A SEA OF CHANGE: ECOLOGY AND OCEANOGRAPHY OF NEW ENGLAND'S FISHING GROUNDS
Rocky and gravelly areas, not found in the western North Atlantic south of New York, are especially important nursery grounds to some of New England's most valuable fisheries such as lobsters, cod, and haddock
The relatively warm regime has a positive effect on cod recruitment and growth (Atkinson et al. 1997, Koslow et al. 1987).
MEASURING PROBABILISTIC REACTION NORMS FOR AGE AND SIZE AT MATURATION
maturation is a complex process that is also influenced by factors other than age and size, such as current resource availability and body reserves
In the real world, however, maturation invariably involves random elements
The concave shape of the established reaction norm (Fig. 5) provides important biological insight about how variation in growth influences the transition of individual fish to maturity. Fish with intermediate growth rate delay their maturation and attain similar or larger sizes at maturation than their fast-growing conspecifics. However, fish with poor growth do not delay their maturation to an extent that would compensate for their slow growth. Proper understanding of plasticity in the maturation of northeast arctic cod may therefore provide us with precious insight into the life-history evolution and dynamics of this stock (Bergstad et al. 1987).
Estimation of these probabilistic reaction norms requires data on both immature and maturing or newly matured individuals. By contrast, the two main traditional approaches, both using the relationship between age and size at maturation, tend to result in estimations that in most circumstances cannot be interpreted as maturation reaction norms but also depend on growth and survival in the considered population
A reaction norm, in general, describes how a single genotype is translated into different phenotypes depending on environmental conditions. In particular, the reaction norm for age and size at maturation characterizes how these two traits respond to environmental variations in growth. Notice, however, that independent environmental variables are not considered for this reaction norm.
We must therefore conclude that published maturation reaction norms are likely to be biased. That bias is directed toward the average growth trajectory; its direction and strength depends on the relative slopes of reaction norms and growth trajectories
sound understanding of maturation dynamics in natural populations will therefore require accurate and unbiased estimations of probabilistic maturation reaction norms. With these reaction norms playing a central role for the dynamics of populations in temporally or spatially heterogeneous environments, achieving such understanding is an important step toward successfully managing and conserving populations in the wild.
Fig. 1.(A) In a deterministic world, maturation would occur when a growth trajectory intersects with the reaction norm for age and size at maturation. (B) In reality, the maturation process is affected by stochastic factors, and observed combinations of age and size at maturation are therefore scattered. This variation is captured by the probabilistic reaction norm for age and size at maturation, defined as the age- and size-specific probability of maturing during a certain time interval (i.e., conditional to being immature at its beginning). The probabilistic reaction norm is illustrated by contour lines for different maturation probabilities (dots on lines). We emphasize that, as introduced in this paper, the reaction norm is defined only at discrete time intervals; the connecting contour lines are for illustration only. (C) At each age, the size-specific maturation probability translates the size distribution before maturation into the size distributions of maturing and immature individuals after maturation*******************************************************************************************
MPA's good because:
maintain age structure (retain older, proportionately more fecund individuals
MPAs can be used as a tool to maintain characteristics of exploited populations (e.g., age, size, and genetic structure), reduce the catch of unwanted species or size classes (i.e., bycatch), maintain species interactions, and maintain characteristics of fish habitat.
role of protecting biodiversity
A model of the effects of an MPA on spawning stock biomass of Atlantic cod on Georges Bank showed that the effectiveness of the MPA is a function of the size of the closed area, fishing mortality outside the reserve, and rates of movement of the target species (Polacheck 1990). For example, greater ranges of movement required larger closed areas to produce net increases in spawning stock biomass because of fishing mortality outside the MPA.
The model results indicate that a reduction in habitat complexity has measurable effects on population dynamics when the adult stock is at low levels (i.e., when spawning and larval survivorship does not produce sufficient recruits to saturate available habitats).
). At high adult population levels, when larval abundance may be high and settling juveniles would greatly exceed habitat availability, predation effects would not be mediated by habitat and no effect in the response of the adult population to habitat change was found.
A model used to determine the effects of an MPA on a sedentary species showed large increases in egg production by sea scallops (Placopecten magellanicus) on Georges Bank based on greater spawning stock biomass (Mcgarvey and Willison 1995).
The effects of current velocity and dispersion greatly reduce fertilization efficiency of broadcast spawners at low densities of individuals, producing Allee effects (Quinn et al. 1993
broadcast spawners |
Fish which release their gametes into the water, where fertilization may occur; without parental care. |
Bycatch and discard of captured fish, juveniles in particular, contribute significantly to population declines (Alverson et al. 1994, Dayton et al. 1995). MPAs sited to protect juvenile size classes of exploited and non-target species could reduce bycatch rates |
Genetic diversity can be preserved if a network of MPAs is designed to prevent fishing local stocks to extinction and to maintain age structure
Capture strategies often select for the larger individuals in a population, producing directional selection. Populations can respond, either phenotypically or genetically, by producing individuals which mature at a smaller size and reduce size at age, hence contributing to growth overfishing (Plan Development Team 1990, Policansky 1993, Ryman and Utter 1987).
). Because fishing mortality often greatly exceeds natural mortality, and exploited species are generally short lived, the selective forces of fishing can produce population changes in relatively short periods of time (Hilborn and Walters 1992).
Significant declines in size at age have been documented for a wide number of exploited species (e.g., Borisov 1979, Garrod and Horwood 1984, Ricker 1981).
However, populations of orange roughy (Hoplostethus atlanticus) off New Zealand experienced significant reductions in genetic diversity over only six years as spawning population size was reduced 70% (Smith et al. 1991).
Nonetheless, size-selective fishing changes the age structure of a population. Older, larger fish are more fecund per unit body weight and therefore contribute more to potential recruitment
They suggest that the intense exploitation of cod, a keystone predator, had cascading effects on populations of epibenthos (e.g., mussels, barnacles, and urchins) which are prey of crabs
In addition to core no-take MPAs, temporary seasonal closures can be used to protect predictable aggregations of adults and juveniles. For example, Atlantic cod have defined springtime shoreward migratory pathways or "highways" off eastern Newfoundland and Labradorwhich follow warm oceanic bottom water entrained in trenches under cold shelf waters (Rose 1993). Adult cod exhibited dense spawning aggregations along the highway.
Protection of nursery habitats requires knowledge of where and when settlement occurs and, in widely distributed species, where juvenile survivorship is highest
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http://ambio.allenpress.com/ambioonline/?request=get-document&issn=0044-7447&volume=034&issue=02&page=0091
Local Fisheries Management at the SwedishCoast: Biological and Social Preconditions
Karl Bruckmeier and Erik Neuman
The picture is similar for the crab, even if some females undertake rather long migrations (31,41). In other marine species, e.g. most flat- and codfishes and eel, which have not only drifting eggs and/or larvae but also spawn in only one or a few areas in a basin, the genetic exchange is still larger.
Genetic Exchange is Very High:
- long migrations
- drifting eggs
- spawn only in a few areas
- migratory as adults
à need large genetic exchange.
àAs they also are migratory as adults, these species are presently not prime candidates for local stock management.
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http://www.gcrio.org/CONSEQUENCES/vol3no1/biodiversity.html
Genetic Population Structure of Fishes: Implications for Coastal Zone Management The pattern for distribution of genetic variation within and between populations is referred to as the genetic population structure of the species
-Species are not genetically homogeneous, but structured into groups of individuals that are typically more or less isolated from one another. Mechanisms that provide isolation include restricted dispersal and homing behavior, i.e. a tendency to return to the place of birth for reproduction
The key issue here is to identify genetically "homogenous" groups of individuals that will constitute the basic units for conservation, management, and sustainable use
Loss of genetic diversity will, depending on the magnitude, hamper future evolution of species and populations more or less seriously and limit their ability to adapt to environmental changes and other interactive pressures. It may also result in immediate reduction of population viability through inbreeding depression, which, in turn, may be followed by declining biological productivity
The geographic area occupied by a particular homogenous group may vary dramatically in size both among and within species as well as over seasons of the year, and this fact should be considered when establishing management regimes.
They frequently result in mixed harvest of hatchery and wild fish, causing overharvest of the wild component. In addition, hatchery fish that differ genetically from the wild ones constitute a genetic threat to natural populations through replacement or hybridization that may cause breakdown of local adaptation and loss of genetic integrity of wild populations (52,53).
, it will result in increased rates of inbreeding and loss of genetic variation through genetic drift
Thus, management strategies that include continuous enhancement to maintain or increase fishery yield are not biologically sustainable and should be abandoned. Basically, releases are genetically justified only in situations aimed at conserving threatened populations that are likely to go extinct, for other reasons than overharvest, if left on their own.
Fishery quotas are largely based on the abundance of released fish, and result in a far too high fishing pressure on the natural populations.
The remaining species for which current information is insufficient from a conservation management perspective include commercially important fishes such as cod and pikeperch. The possible structuring of cod populations within the Baltic has been an issue for a long time, but comprehensive genetic studies are yet not available. Current information suggests that the cod shows little differentiation within the Baltic, but like other marine species the Baltic cod is genetically distinct from that of the Atlantic(75)
as i)_distinct populations; _ii) continuous change; and iii) no differentiation***************************************************************************************************************http://www.bioone.org/perlserv/?request=get-document&doi=10.1656%2F1092-6194%282000%29007%5B0317%3AFIASOC%5D2.0.CO%3B2
FISHERIES IN A SEA OF CHANGE: ECOLOGY AND OCEANOGRAPHY OF NEW ENGLAND'S FISHING GROUNDS
Rocky and gravelly areas, not found in the western North Atlantic south of New York, are especially important nursery grounds to some of New England's most valuable fisheries such as lobsters, cod, and haddock
The relatively warm regime has a positive effect on cod recruitment and growth (Atkinson et al. 1997, Koslow et al. 1987).