Essay on Biological and Operational Interactions Between Marine Mammals and Global Fisheries

Published: 2021/11/30
Number of words: 1683


The interaction between fisheries and marine mammals has spanned a long time now. The interaction between the marine mammals and fisheries is usually classified into either biological (ecological) or operational interactions (Gaichas et al., 2016). Ecological interactions happen when both the marine mammals and the fisheries are competing for the same prey (Winemiler, 2017). That is they rely on the same source of food. Additionally, the transmission of parasites between the marine mammals and the fisheries is the other form of ecological interaction. Operational interactions are those in which the marine mammals damage the fishing gears and interfere with the whole fishing process (Jennings, 2016). In some instance, the marine mammals may take fish from the commercial fisheries.The topic has attracted the interest of many researchers who seek to know the effects of the relationship between the two. Having mentioned the relative importance of the subject.In this paper, we will concern ourselves with a comprehensive analysis of the relationship between the global fisheries and the marine mammals.Besides, the article will also explore the implications of the relations between the two.Specifically, the paper will look at what constitutes either biological or functional interactions by giving examples.

Biological interactions

The ecological interactions between marine mammals and fisheries may be either direct or indirect (Jackson, 2015). A direct interaction occurs when the marine mammals feed on the fisheries themselves. Indirect interaction occurs when both compete for the same prey as the source of the food. The two sets of interaction have an aspect of competition attached to them.

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Transmission of parasites

Some of the marine mammals act as carriers of certain parasites, which they, later on, transmit, to other fish species. The parasites transmitted affect the health of the fish adversely reducing their marketability (Authority, 2015). In some cases, the parasites from the marine mammals have been shown to cause death on the part of the fish. In this case, the marine mammals act as an intermediate host to the parasites. A typical example is the Porrocaecum deciphens otherwise known as the codown.The gray seal (Halichoerus gryphus) transmits Codowns into other fish (Nadlona-Altyn, Podolska, Szostakowska, 2017).The parasite infects muscle tissues of other fish reducing their value. Vast populations of Gadus Morhua (cod) have been affected by the codown nematode.


The population of marine mammals has been on an unabated increase in recent years (Pacifici et al., 2017). In fact, their population is estimated to be growing at a rate of 5% and 10 % per annum; which is due to the reduction in the overexploitation of these species. Also, the view whether marine mammals should be harvested has contributed significantly to their increase in the population. According to FAO (Food Agriculture Association), more than 950 million people in the world feed on fish. The fish accounts for at least a one-third of their source of meat. It is also essential pointing out that the marine mammals feed on these fish also. In the 1990s in the southern African region, the Arctocephalus pusillus ptisillus (Cape fur seals) was estimated to consume two million tons of food annually (Fallows, Benoit &. Hammerschlag,2015).The exciting bit is the annual consumption of the cape fur seal was equal to the total catch of fish by humans in the area. Because the population of the marine mammals has been on the increase, it is clear that conflicts have risen between the two in recent years. Another example is in the Pacific seas where marine mammals consume close to 150 million tons of food each year (Shuntov & Ivanov,2015). This is four times the annual human consumption of fish from the Pacific Ocean. Again Since the 1990s, the populations of the Harp seal has been on the increase in the east coasts of Canada. The harp seal fed on the massive population of the Juvenile cod present in the area. In the end, this reduced significantly the Cod population, which in the end forced over 40000 fishers out of work (Hutter,2015).

Operational Interactions

Gear Damage

The damage to fishing gear occurs when the marine mammals are entangled when trying to free fish caught in nets or hooks (Helker et al., 2017). In the process, this damages the fishing gear leading to loses as the damaged fishing gear cannot fish efficiently. Besides when attempting to free the fisheries caught, the marine mammals maybe victims of bycatch. More damage is usually reported on static fishing gear such as traps and long lines (Wang, Wang, & Wang, 2017). For the moving equipment like purse seining and trawling, there is reduced damage.Pinnipeds have been reported numerous times to impair with fishing gears. In some isolated situations, the destruction is accidental. For example in 1970, on the east shores of Canada, Humpback whales caused damage worth millions of dollars by unintentional collisions with the cod traps (Krebs, 2016).


Marine mammals have repeatedly been shown to disrupt fishing operations. They have been known to scatter away from the fish with their movements. In some cases, they also try to feed on the fish caught. For examples, the movement and diving acts of cetaceans and Pinnipeds usually cause shoals of fish to disperse away and escape being caught (Secor, 2015). In most of the times, fishers typically try to locate their fishing gears far away from the marine mammals. In some instances, anglers have been reported to relocate their fishing gears due to the presence of the marine mammals, which is costly and time wasting. Again as earlier mentioned some of the marine mammals maybe victims of bycatch.There are numerous cases of seals caught in fishing expeditions. In an attempt to free itself from the net, the seal damages the fishing gear and in some cases may injure some of the anglers (Werner, Northridge & Young, 2015). In such a case, the fishermen are forced to rearrange their fishing expedition again.


Marine mammals have been shown to cause depredation (Trites & Spites, 2016). Depredation refers to the act of the marine mammals feeding on the already caught fish. They may either feed on the whole fish or in some cases feed on a part. Overall, this makes the fish caught unsalable. According to Yano and Dahleim (1995) because of depredation, losses range between 25 % and 100 % of the total catch. The Zalophus Caliofarnus has been reported to depredate on logline-caught fish. Again, due to learning, some of the marine mammals have been shown to emulate human beings on the use of the fishing gear. They use the fishing gear in trying to catch fish and playing with fish. In the end, this results in damage to the fish. The damaged fish go to waste since they are not useful to the anglers.

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Lastly, evidence from various studies shows species of Marine mammals such as Cetaceans and Sirenians are usually attracted to fishing gears. They try to remove the bait from the fishing gears which results in massive losses on the part of the anglers as the fishing gears more often are damaged.


In conclusion, we have examined the various forms of interactions between global fisheries and marine mammals. It is worth noting with the population of marine mammals sets to increase; the interactions will be significantly influenced. The increased interactions may lead to a reduction in the population of either of the two. It is little wonder various marine societies have stepped in and tried to put multiple control measures.


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