Impacts of environmental change and direct and indirect harvesting effects on the dynamics of a marine fish community

2008 ◽  
Vol 65 (10) ◽  
pp. 2088-2104 ◽  
Author(s):  
Hugues P. Benoît ◽  
Douglas P. Swain
Keyword(s):  
Marine Fish ◽  
Fish Community ◽  
Prey Availability ◽  
A Priori ◽  
Small Fish ◽  
Trawl Survey ◽  
Ecological Traits ◽  
Ocean Climate ◽  
Selected Traits ◽  
Catch Rates

We describe dramatic shifts in the species composition of the marine fish community of the southern Gulf of St. Lawrence using a 35-year time series of catch rates in an annual bottom-trawl survey. We attempt to understand the causes of these changes using a traits-based approach that relates the similarity among species in their abundance trends to similarities in their ecological traits. We selected traits based on a priori beliefs of how each should reflect susceptibility to changes in a different external factor potentially affecting the community. We found evidence for an effect of ocean climate and top-down effects of fishing and seal predation, but not for bottom-up effects of prey availability on adult fishes. Mean body length in the community decreased dramatically in the 1990s. This reflected the removal of large-bodied fishes by fishing and sharp increases in the abundance of small fishes. The biomass of small fish was inversely correlated with an index of predation on those fish by larger fish, suggesting strong predator control of the abundance of small-bodied fishes. Our results suggest that changes in ocean climate combined with direct and indirect effects of harvesting can dramatically and rapidly alter the composition of marine fish communities.

Maternal attendance patterns of Steller sea lions (Eumetopias jubatus) from stable and declining populations in Alaska

2003 ◽  
Vol 81 (2) ◽  
pp. 340-348 ◽  
Author(s):  
Linda L Milette ◽  
Andrew W Trites
Keyword(s):  
Prey Availability ◽  
A Priori ◽  
Population Decline ◽  
Perinatal Period ◽  
Eumetopias Jubatus ◽  
Steller Sea Lions ◽  
Sea Lions ◽  
First Feeding ◽  
Attendance Patterns ◽  
The Mean

Maternal attendance patterns of Alaskan Steller sea lions (Eumetopias jubatus) were compared during the summer breeding seasons in 1994 and 1995 at Sugarloaf Island (a declining population) and Lowrie Island (a stable population). Our goal was to determine whether there were differences in maternal attendance between the two populations that were consistent with the hypothesis that lactating Steller sea lions in the area of decline were food-limited during summer. Our a priori expectations were based on well-documented behavioural responses of otariids to reduced prey availability. We found that foraging trips were significantly shorter in the area of population decline, counter to initial predictions. The mean length of foraging trips in the declining area was 19.5 h compared with 24.9 h in the stable area. In contrast, the mean perinatal period (time between parturition and first feeding trip) was significantly longer in the area of decline (9.9 versus 7.9 days), again countering initial predictions. The mean length of shore visits for the declining population was also significantly longer (27.0 h compared with 22.6 h where the population was stable). For both populations, the mean time that mothers foraged increased as pups grew older, whereas the time that they spent on shore with their pups became shorter. Behavioural observations of maternal attendance patterns are inconsistent with the hypothesis that lactating Steller sea lions from the declining population had difficulty obtaining prey during summer.

Grenadiers of the World Oceans: Biology, Stock Assessment, and Fisheries

2008 ◽  
Keyword(s):  
Continental Slope ◽  
Ross Sea ◽  
Stock Assessment ◽  
Trawl Survey ◽  
Factors Affecting ◽  
Year Effect ◽  
Macrourus Whitsoni ◽  
Catch Rates ◽  
Potential Methods ◽  
Major Factors

<em>Abstract</em>.—An exploratory longline fishery for toothfish (<em>Dissostichus </em>spp.) in the Ross Sea, Antarctica has been carried out since 1997. The main bycatch species in this fishery is the grenadier, <em>Macrourus whitsoni. </em>No assessments have been carried out of the impact of the fishery on grenadiers, although they have life history characteristics that make them vulnerable to overexploitation. The aims of this research were two-fold; firstly, to characterize the bycatch fishery and to determine factors affecting bycatch rates; and secondly to examine potential methods of monitoring its abundance. A standardized CPUE analysis was used to determine factors affecting bycatch rates of grenadiers in the fishery. The analysis was based on fine-scale haul-by-haul data from all vessels in the fishery from 1999 to 2005. The major factors influencing grenadier bycatch were vessel, area, and depth. Catch rates of grenadiers were highest along the continental slope of the Ross Sea in depths from 600 to 1000 m, and there was an order of magnitude difference in grenadier catch rates between different vessels. Examination of vessel characteristics showed that catch rates of grenadiers were significantly lower with the Spanish line system than with the autoline system. There are several plausible reasons for this difference, including hook location with respect to the seabed, bait type, and differences in levels of reporting of bycatch between vessels. Various approaches to monitoring and assessing grenadiers in the Ross Sea fishery were explored. We conclude that the year effect from the standardized CPUE analysis is unlikely to be monitoring abundance but instead probably reflect changes in gear characteristics, fisher behavior, and targeting of effort. Trends in the length composition of the catch are confounded with depth, and are also of limited value at present. We consider that the best approach to obtaining abundance estimates for grenadiers in the Ross Sea would be to carry out a random bottom trawl survey of the continental slope.

scholarly journals Limited mid-water scavenging of trawl discards

2003 ◽  
Vol 83 (4) ◽  
pp. 731-734 ◽  
Author(s):  
Karim Erzini ◽  
Pedro Monteiro ◽  
Artur Araújo ◽  
Margarida Castro
Keyword(s):  
Water Column ◽  
Deep Water ◽  
Small Fish ◽  
Sea Birds ◽  
Trawl Fishing ◽  
Southern Portugal ◽  
Catch Rates ◽  
Electric Fishing ◽  
Scavenging Rates

The consumption or scavenging of fish in the water column at depths from 75 to 275 m in Algarve (southern Portugal) trawl fishing grounds was evaluated. Longlines were used to suspend baits throughout the water column while electric fishing reels were used to simulate sinking discards. Eighteen species were caught, with higher catch rates near the surface than near the bottom. However, scavenging rates were generally highest near the bottom and lowest in the middle of the water column. At depths less than 100 m the majority or all the fish were scavenged throughout the water column, while at depths greater than 200 m most of the fish were untouched after periods of time greater than would be required for them to sink to the bottom. Since other studies have shown that most small fish discards are scavenged at the surface by sea birds and most of the discarded species that sink are either too large or not attractive to pelagic predators, these results suggest that mid-water scavenging of trawl discards in deep water is relatively unimportant.

Rapid winter warming could disrupt coastal marine fish community structure

2020 ◽  
Vol 10 (9) ◽  
pp. 862-867
Author(s):  
Nicholas J. Clark ◽  
James T. Kerry ◽  
Ceridwen I. Fraser
Keyword(s):  
Community Structure ◽  
Marine Fish ◽  
Fish Community ◽  
Fish Community Structure ◽  
Winter Warming ◽  
Coastal Marine

Fish Introductions in Africa and Some of Their implications

1991 ◽  
Vol 48 (S1) ◽  
pp. 8-12 ◽  
Author(s):  
Richard Ogutu-Ohwayo ◽  
R. E. Hecky
Keyword(s):  
Endemic Species ◽  
Algal Blooms ◽  
Fish Community ◽  
Trophic Ecology ◽  
Spatial Scales ◽  
Introgressive Hybridization ◽  
Small Fish ◽  
Fish Ponds ◽  
Food Web Structure ◽  
Fish Introductions

Fish introductions in Africa have been made at various spatial scales from small fish ponds to the largest lakes, primarily to sustain or increase production, though some were to develop sport fisheries and to control unwanted organisms. Some introductions have fulfilled their objective in the short term, but several "successful" introductions have created uncertainties about their long-term sustainability. Lates niloticus, Oreochromis niloticus, O. leucostictus, Tilapia melanopleura and T. zilli were introduced into Lakes Victoria and Kyoga in 1950's and early 1960's; by the 1980's L. niloticus and O. niloticus dominated the fisheries, having virtually eliminated a number of endemic species. In Lake Victoria, the loss of genetic diversity has been accompanied by a loss of trophic diversity; the transformation of the fish community coincided with profound eutrophication (algal blooms, fish kills, hypolimnetic anoxia) which might be related to alterations of the lake's food-web structure. By contrast, the introduction of a planktivore, Limnothrissa miodon into Lake Kivu and the Kariba reservoir has established highly successful fisheries with little effect on the pre-existing fish community or trophic ecology. The endemic species-rich African Great Lakes may be particularly sensitive to introductions. Species extinctions, introgressive hybridization and ecosystem alterations may occur following introductions.

scholarly journals A Survey On Marine Fish Species In River of Mahakam East Kalimantan, Indonesia

Omni-Akuatika ◽  
2017 ◽  
Vol 13 (2) ◽  
Author(s):  
Iwan Suyatna ◽  
Muhammad Syahrir ◽  
Mislan Mislan ◽  
Yuni Irawati Wijaya ◽  
Abdunnur Abdunnur
Keyword(s):  
Marine Fish ◽  
Fish Species ◽  
Water Depth ◽  
Fish Community ◽  
Marine Species ◽  
Demersal Fish ◽  
Middle Part ◽  
Marine Fish Species ◽  
East Kalimantan ◽  
Velocity Water

A first survey  on a community marine species in  river of Mahakam East Kalimantan was performed in December 2015 and May 2016. Fish samplings were carried out from two locations the lower and the middle part of Mahakam. Whilst hydrometric observation of current velocity, water depth and tide was measured not only at the locations but also along the river from 2013 to 2017, tide was only observed in the lower part of Mahakam.  However, marine fish species were recognized to reach up the middle part of Mahakam, 230 km from coastline.  To describe a community fish structure and its dissimilarity of the two surveyed locations, diversity and bray Curtis index were applied.  Almost 15 marine fish species identified in river of Mahakam was demersal fish and index of the similarity of marine fish community between the locations only 0.106.

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