In this post, I will outline some of the main ideas of various scholarly literature (limited to publications released since 2000, unless research regarding a specific topic is unavailable) regarding salmon management in the UK, with Scotland as a focus. I chose western Europe, the UK, and Scotland as a geographic focus for my concentration because of my experience studying at Aberdeen University in 2014-2015. At Aberdeen, I had the opportunity to live close to one of the main salmon production powerhouses of the world, and this piqued my academic interest in the subject of salmon. While all literature mentioned below were given equal examination, some were more relevant than others, contributing to an unequal expansion on each study.
An Introduction to Scotland’s Salmon Scene
The Scottish Salmon Producers Organisation (SSPO) is the trade association responsible for representing “industry-wide initiatives… public information [and] a strong industry voice” for the massive Salmon industry based out of mainland Scotland, Shetland, Orkney, and the Western Isles. The Scottish salmon industry, which in 2014 produced the country’s record-breaking 179,022 tonnes of farmed Atlantic salmon, is among the top producers globally for salmon, and naturally, the product is the country’s (and the UK’s) highest export product. According to recent publications from the Scottish Government, the aquaculture scene is planning to diversify its focus from mainly Atlantic salmon by increasing brown/sea trout Salmo trutta and halibut Hippoglossus hippoglossus farming in 2015. Understandably, this economically vital industry is dynamic in its approach to solving issues regarding aquaculture such as lice, disease, and contaminants. One of the current efforts mentioned in Marine Scotland Science’s Scottish Fish Farm Production Survey 2014 is biological control of parasites (sea-lice) by utilizing wrasse and lumpsuckers. Scientific research by the University of Stirling’s Institute of Aquaculture is conducted on these cleaner wrasse, and I will look further into this topic by reviewing the available scientific literature. As a side note, 95% of salmon produced in Scotland comes from farms represented by the SSPO; thus, salmon-related research understandably is connected, if not funded, by SPPO; in continuing research on Scottish salmon, we must be weary of the industry’s hand in scientific research. At this link, you can find a short BBC News segment on cleaner wrasse studies.
Sea Lice Infestations: A Rut in the Road for Viable Salmon Aquaculture
In this 2002 study of sea lice infestations in Scotland, we first find the stark effect of sea lice on wild finfish populations, costing an estimated “15-30 million per annum in control measures and lost production.” According to cited literature, mortality rates range from 30-50% for trout smolts and 48-86% on wild salmon smolts. Understandably, as the the aquaculture industry grows, it must address this key issue through effective management strategies. The study utilizes a model to understand the source of infestations and epizootics, and the results point to farmed salmon as the primary hosts for sea lice, “producing at least 78% of eggs, and at most 97%.” According to 3 separate literature cited in the study, salmon and trout smolt mortality is the reason behind declining stocks in the west coast of Scotland, but confounding factors such as climate change are too abundant to point to a single major factor that is causing declines. However, the study’s findings of overigerous louse presence on farmed fish vs. wild fish (high vs. low) and the cited literature of smolt mortality as a function of overous louse presence on individual fish (high when high) alludes to a very telling relationship: farmed fish host high density parasitic sea lice, which can be transmitted to wild populations, causing wild stocks to crash. The study notes that a “louse target of <0.005 per farm salmon was necessary to minimise the risk of transmission to wild salminoids” in the studied time frame. The study concludes by voicing the importance of controlling sea lice on farms and curtailing transmission of sea lice from farmed fish to wild stocks.
In this 2008 study of the efficacy of the most widely used treatment against sea lice finds finds that sea lice develop an increased resistance to emamectin benzoate (incorporated into fish feed), necessitating the rotation of treatment methods.
The Atlantic Salmon’s Upstream Migration: Artificial Obstacles
Although fish conservation in the UK seems to focus on utilizing farmed fish, wild fish, and the study of wild fish, is just as important. Thus, I have done looked into some literature regarding Scotland’s research of wild fish.
In this 2002 study of the obstacles preventing or slowing the Atlantic salmon’s return to their spawning grounds illustrates the need to effectively manage freshwater “highways” for anadromous fish. 54 tagged fish were monitored through their journeys upstream, yet only four reached their spawning grounds. Fish pass complexes were incorporated in the routes to aid in navigating around man-made structures, but cumulative factors of stress, pathogens/fungal infection, high energy requirements to jump over fish ladders, natural light availability (if fish are caught in fish ladders after daylight, they will stay there and suffer high energy costs to maintain their position against the flow of the river before proceeding when the daylight returns), otter predators, and confusion of paths due to the mixing of water from different rivers. The study’s findings, when aligned with related literature, is that “fish passage facilities [should be] constructed so that they are as easy as possible for fish to pass through.”
Solutions from the Primary Literature
Understandably, Scotland is a hub for research concerning cutting-edge techniques to solving aquaculture’s problems, but the coastal countries of western Europe, namely Norway, also conducts valuable experiments. In this 2013 study at the Institute of Marine Research in Norway, scientists examined the efficacy of wild and farmed cleaner wrasse in consuming parasitic sea lice on salmon. Incredibly, their experiments began yielding significant results within the end of the first week; control cages of salmon without cleaner wrasse produced high sea lice concentrations (average 9 lice per fish) while that of treatment cages remained low (average <1 lice per fish). Furthermore, the results were not significantly different among treatment cages, which alludes to an extremely high effectiveness of both wild and farmed cleaner wrasse in removing sea lice. The study concludes by recommending further research on the optimal wrasse:salmon ratio (25:500 in this experiment) so as to prevent undernourishment of the wrasse leading to weight loss. Additionally, future research should focus on the efficacy among different species of wrasse, so when implementing wrasse in aquaculture programs, the most effective wrasse species will be chosen. Scottish public opinion about aquaculture favors high environmental responsibility for farmed salmon producers, and utilizing cleaner wrasse (wild or farmed) is a promising solution to one of salmon aquaculture’s most prevalent problems. Scotland continues its search for viable solutions with further wrasse research and other innovative ideas.
Other Literature soon to be reviewed:
http://onlinelibrary.wiley.com/store/10.1046/j.1439-0426.2000.00260.x/asset/j.1439-0426.2000.00260.x.pdf?v=1&t=if9571lf&s=8174ff5913e01b7041da779a1f393192d7b97b5d