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Design of a Marine Protected Area in Öresund (Baltic Sea) and its effects on population of Atlantic cod (Gadus morhua)

Orfanidis, Georgios (2016) BION01 20152
Degree Projects in Biology
Abstract
Marine protected areas (MPA) have been widely used the recent years, as an alternative to the traditional management tools, in order to increase the yield and the health of a stock. The present study shows how cod population in Öresund would respond under different spatial and temporal MPA and how they will affect the gill-net fisheries in the area. For that reason, a simple model, based on logistic growth, and an age structure model were formulated using as initial inputs the results of a sub-stock assessment for the specific stock. The results supported that environmental stochasticity should be included in the models, as it may affect the recruitment and the general state of the stock. Moreover, the reserve in nursery areas exhibited... (More)
Marine protected areas (MPA) have been widely used the recent years, as an alternative to the traditional management tools, in order to increase the yield and the health of a stock. The present study shows how cod population in Öresund would respond under different spatial and temporal MPA and how they will affect the gill-net fisheries in the area. For that reason, a simple model, based on logistic growth, and an age structure model were formulated using as initial inputs the results of a sub-stock assessment for the specific stock. The results supported that environmental stochasticity should be included in the models, as it may affect the recruitment and the general state of the stock. Moreover, the reserve in nursery areas exhibited the best scenario in order to increase the stock biomass, the yield and ultimately the gross revenues in fisheries. However, the plethora of the scenarios supported that Öresund cod fisheries could not be further developed due to the healthy state of the stock, giving space only for technical regulations, catch and effort control or a combination of the above. (Less)
Popular Abstract
Marine protected areas (MPA) have been widely used the recent years, as an alternative to the traditional management tools, in order to increase the yield and the health of a stock. The positives of the MPA in fish stock biomass have been presented by previous studies and include higher recruitment rates, enhancement of the adjacent areas through spillover and many more. The Atlantic cod stocks (Gadus morhua) in Oresound (Baltic Sea) have been harvested since ancient years and it is considered to be a negligible part of the western Baltic cod stock. Recent studies have shown that Oresound’s cod stock forms an independent stock. Oresound is a partially protected area due to a trawling ban since 1932, allowing the cod stocks to thrive.

... (More)
Marine protected areas (MPA) have been widely used the recent years, as an alternative to the traditional management tools, in order to increase the yield and the health of a stock. The positives of the MPA in fish stock biomass have been presented by previous studies and include higher recruitment rates, enhancement of the adjacent areas through spillover and many more. The Atlantic cod stocks (Gadus morhua) in Oresound (Baltic Sea) have been harvested since ancient years and it is considered to be a negligible part of the western Baltic cod stock. Recent studies have shown that Oresound’s cod stock forms an independent stock. Oresound is a partially protected area due to a trawling ban since 1932, allowing the cod stocks to thrive.

Goal of the specific study was to investigate the effects of designing different types of MPA in cod stocks and in gill net fisheries. For that reason I modelled the cod stock in Oresound based on existing fisheries and scientific data. The models included the simple model based on logistic growth and the age structured model which assumes that each age class follows an exponential decay through time. For the simple model, projections for the following year were done including stochasticity for carrying capacity (K) or by changing the K. For the age structure model projections of different MPA types were carried out, such as protecting only the nursery areas, the feeding and the nurseries or temporal closure in the entire area. Also, the gross revenues from the catch in each scenario were estimated based on prices obtained by Swedish vessels in 2009.

The stock assessment revealed that cod stock fishing mortality was high but during the last years decreased. Regarding the simple model, the changing values of K within and outside the MPA didn’t affect the equilibrium total stock biomass (TSB) and the yield. Also, the environmental stochasticity decreased the mean value of the TSB and it increased the uncertainty as it may affects the recruitment and the general state of the stock. On the age structure model the highest yield observed under the scenarios of without any reserve area and with reserve in nursery areas. The highest TSB observed in the largest MPA, while seasonal closures exhibited the highest value of maximum sustainable yield (MSY). Moreover, the age structure of the stock differed between the scenarios. The proportion of the older-biggest individuals in total stock increased in scenarios of mixed reserved areas and seasonal closure. The scenario of nursery areas reserve it was exhibited the highest gross revenues in gill net fisheries, while the lowest for seasonal closure and mixed reserves.

To conclude, I suggest that environmental indices should be included in simulations for more realistic recruitment and potential nursery areas predictions. In addition, I acknowledge that even though the cod stock in Öresund will increase with the creation of any type of reserve, the gill net fisheries could not be further developed, even for the case of protecting the nursery areas as its implementation would be difficult. Instead there are opportunities for technical regulations, catch and effort control or a combination of different methods to improve the value of the catch and simultaneously increase stock size.

Advisor: Anders Persson
Master’s Degree Project in Biology 45 credits 2016
Department of Biology, Lund University (Less)
Please use this url to cite or link to this publication:
author
Orfanidis, Georgios
supervisor
organization
course
BION01 20152
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
8891837
date added to LUP
2016-09-15 14:29:18
date last changed
2016-09-15 14:29:18
@misc{8891837,
  abstract     = {Marine protected areas (MPA) have been widely used the recent years, as an alternative to the traditional management tools, in order to increase the yield and the health of a stock. The present study shows how cod population in Öresund would respond under different spatial and temporal MPA and how they will affect the gill-net fisheries in the area. For that reason, a simple model, based on logistic growth, and an age structure model were formulated using as initial inputs the results of a sub-stock assessment for the specific stock. The results supported that environmental stochasticity should be included in the models, as it may affect the recruitment and the general state of the stock. Moreover, the reserve in nursery areas exhibited the best scenario in order to increase the stock biomass, the yield and ultimately the gross revenues in fisheries. However, the plethora of the scenarios supported that Öresund cod fisheries could not be further developed due to the healthy state of the stock, giving space only for technical regulations, catch and effort control or a combination of the above.},
  author       = {Orfanidis, Georgios},
  language     = {eng},
  note         = {Student Paper},
  title        = {Design of a Marine Protected Area in Öresund (Baltic Sea) and its effects on population of Atlantic cod (Gadus morhua)},
  year         = {2016},
}