Salmon Watch Ireland Conference - Hatcheries and Stocking

Salmon Watch Ireland hosted its annual conference on the 21^st of November 2015 in the Ballsbridge Hotel, Dublin.

The 2015 conference, entitled “Hatcheries and Stocking- have they a role in restoring salmon stocks”, investigated the potential role of stocking in restoring Ireland's dwindling stocks of Atlantic salmon. 

The official opening was conducted by Mr. Alex White, Minister for Communications, Energy, and Natural resources. Following introductory remarks from SWIRL chairman Niall Greene, five talks were given by experts in salmon ecology, conservation, and stocking.  Each talk was followed by a discussion period in which attendees brought their own varied perspectives to the table, sparking some healthy debate.

Salmon Watch Ireland Conference - Official Opening

Minister Alex White began the proceedings with an enlightening description of the status of salmon within the context of medieval Irish Brehon Law. Mr. White stated that Ireland was one of the first countries to enshrine rights to salmon into its legislation, a historical fact which highlights the long-standing cultural and economic importance of the species to the Irish people. Against this background, Mr. White said, Ireland applies a precautionary approach to the conservation of wild salmon.

In particular, he assured the attendees, the Department of Communications, Energy, and Natural Resources would only support development which is found to be environmentally sustainable and which won’t damage wild salmon stocks. Turning his focus to the particular issue of stocking, Minister White stated that he is aware of serious concerns regarding the potential negative impacts of stocking on the genetics of wild salmon populations.

In keeping with the application of a precautionary approach to the conservation of wild salmon, Minister White concluded that the maintenance of genetic diversity within the species is of paramount importance. This key sentiment was echoed by the majority of the subsequent speakers.

Introductory Remarks

Niall Greene of SWIRL gave a brief introduction to the conference. During his introduction Mr. Greene explained that this year’s conference topic was chosen in response to increased debate over stocking issues which has stemmed from the worrying decline of wild Atlantic salmon throughout much of their range.

Although a number of very eminent fishery scientists were on hand to share their research and perspectives on the issue of stocking, no managers of fisheries with current hatchery programs were in a position to speak at the conference.

Talk 1

“To Stock or Not to Stock”

Dr. David Solomon

Dr. David Solomon’s talk began with a brief outline of the current state of British and Irish salmon stocks. From his perspective, the present status of these stocks is less dire than many people believe. A key point which Dr. Solomon and subsequent speakers emphasized was that salmon stocks are generally highly resilient, and are capable of bouncing back after periods of dramatic decline.

While, to his knowledge, no rivers in the British Isles have entirely lost their salmon stocks in recent decades, a significant number have actually reestablished populations that had previously been extirpated. According to Dr. Solomon, there are probably salmon spawning in more rivers throughout the British Isles at present than at any other time over the last 200 years. Water quality and migratory access are generally improving, and river specific harvest quotas are calculated and enforced.

Factors Within Rivers

Prior to any serious consideration of establishing a salmon stocking programme, Dr. Solomon told the audience, we must first identify the factors which currently limit the production of salmon within the river system and, if feasible, remedy these issues.

Such issues may include water quality, water abstraction, obstructions to migration, habitat degradation, altered flow regimes, or over-exploitation of the salmon stock itself. This approach, whereby you “look after the environment and the fish will do the rest”, was strongly advocated by all subsequent speakers at the conference and is widely regarded as the safest, most effective, most enduring, and usually the cheapest way of increasing salmon stocks. Of course, by improving the habitat within and around river systems there are additional benefits to local biodiversity, water quality, and overall ecosystem function.

In talk 4, Dry Stephen Marsh-Smith outlined an extremely ambitious and successful rejuvenation project he has been involved with on the river Wye. This project, which is currently ongoing, has allowed salmon to utilize huge areas of river that had been unsuitable or inaccessible to them for decades if not centuries.

The result has been a highly significant increase in fish numbers, angling catch rates, and utilized spawning habitat without any reliance on stocking programmes.

Against this background, the first question Dr. Solomon sought to answer is “Why to stock?” In response to this question, Dr. Solomon proposed 6 circumstances in which stocking might be considered, and gave his thoughts on the benefits and risks associated with stocking in each case. Broadly speaking, these 6 circumstances may be divided into 2 main categories:

Two Categories

Firstly, stocking where no wild population currently exists, and secondly, stocking in a river already populated by a wild population.

In the first category, it is highly likely that appropriate conditions for salmon spawning, rearing, or migratory access are currently absent from the river system (hence the absence of wild salmon). If such environmental conditions cannot be created, any stocking programme will fail to establish a self-sustaining wild population. The only realistic application of this approach is to “ranch” salmon for recreational or commercial fishing, a concept which was dealt with in detail by Dr. Ken Whelan in Talk 5.

The second category proposed, in which the aim is to augment the number of salmon within an existing wild population by establishing a stocking programme, is perhaps the most important within the context of declining wild Irish stocks. It is perhaps also the more contentious of the two applications of stocking.

While Dry Solomon believes the case against stocking in these circumstances is often overstated, in Talk 3 Professor Carlos Garcia de Leaniz presented compelling evidence that stocking in this circumstance is fraught with real long-term dangers to the native wild population.

A number of rivers were mentioned which had apparently successful hatchery programmes but  which have given rise to uncertainty in regard to the role they played in rehabilitation. It was found that many fish which re-colonised these rivers (Taff, Neath and Tawe in South Wales, the Tyne in NE England, the Lagan in Northern Ireland, and the Clyde in Scotland) which had hatcheries were in fact strays from nearby rivers taking advantage of the removal of limiting factors. The remnants of a wild population in these rivers may also have contributed to the rebuilding of stocks (Tyne).

Another reason to stock examined was the manipulation of the genetic makeup of the stock with MSW salmon runs being increased in catchments to increase the runs of these fish. This needs to be well supervised and monitored to achieve success.

Finally the stocking of fry in rivers to attract straying salmon was mentioned as a possible method to provide pheromones to attract salmon into rivers.

Define the Problem

Dr. Solomon concluded his talk by telling the attending salmon enthusiasts that, “in deciding whether or not to stock, there is a need for absolute clarity in defining the problem, the objectives of any programme, assessing the limiting factors that are restricting natural production, identifying how the proposals will remove or bypass these limiting factors, and an assessment of the risks.” As such, the potential merits or risks of stocking must be assessed on a case-by-case basis.

TALK 2:

“Hatchery licencing and regulation in Ireland”

Dr Michael Millane, IFI

In the second presentation of the day, Dr. Millane of Inland Fisheries Ireland gave a concise and practical summary of the requirements involved in applying for hatchery licenses in Ireland. This was followed by a brief history of salmon management and stocking in Ireland, and an explanation of the current advice given by both IFI and NASCO in relation to salmon management.

In the Republic of Ireland, all salmon hatcheries are designated as aquaculture. The Department of Agriculture, Food and the Marine acts as the sole regulatory authority of aquaculture while the Minister for Agriculture, Food and the Marine is responsible for accepting or rejecting all hatchery applications. The criteria used to assess license applications were discussed in some detail, as were the legal obligations of the hatchery license holder.

River Categories

Dr. Millane told the audience that IFI echoes NASCO’s guidelines on stocking. These state that no Atlantic salmon reared in a fish culture facility should be released into a Class I river (Class I rivers, of which Ireland has many, are considered to have no significant human induced habitat alterations and no history of stocking).

Research has shown that in Class II and III rivers (which exhibit varying levels of habitat degradation) the long term cost of producing additional adult salmon and trout using habitat enhancement programmes is generally only a fraction of the costs one would incur while trying to generate the same increases through stocking programmes. There are also serious concerns over the potential negative impacts of stocked salmon on wild populations from a genetic, ecological, and disease transfer perspective.

Against this background, IFI’s advice on the enhancement of Irish salmon stocks is to support habitat enhancement schemes rather than artificial stock enhancement programmes which have the potential to detrimentally impact locally adapted wild populations.

Habitat Enhancement

Dr. Millane also outlined simple measures, such as gravel improvement and augmentation, can be implemented for modest cost which can lead to additional breeding habitat.  Bank restoration by fencing and planting is also of great importance as it enables the river to return to its natural flow. 

Narrowing river width by keeping cattle out of certain stretches can increase stream flows which prevents silt from settling on important gravel sections.   Obstacles such as dams and impassible sections of river can be opened up to create more spawning and breeding areas. 

Restoring rivers and the upper dendrite streams especially can have very significant benefits which increase the number of redds and spawning success. (IFI grant aid can be obtained in Ireland for river improvements and the benefits are considerable). 

TALK 3

There are no salmon in the Yemen 

 Professor Carlos Garcia de Leaniz, University of Swansea

In the third talk, Professor Carlos Garcia de Leaniz emphatically argued against the use of stocking as tool for restoring wild salmon populations.

He began by citing his own research which found that, despite very high juvenile survival rates within the hatchery environment, 62% of hatchery pairings resulted in no adult returns at all. De Leaniz found that hatchery environments negate the effect of natural selection, allowing weak and mal-adapted fish to survive until they are released.

Up to 86% of hatchery parr were found to be asymmetrical, compared with only 10% in the wild, while body shape, coloration, and fin length of hatchery reared fish become increasingly mal-adapted for the natural environment the longer they live in a hatchery.

Increased Mortality

Once in the wild, hatchery-reared fish exhibit extremely high mortality rates compared with their wild counterparts. The vast majority of asymmetric individuals die within 50 days. Thus, the high survival rates initially encountered within the hatchery environment may largely be offset by dramatic mortality once the fish are released.

According to Professor de Leaniz, the more hatchery fish that are released in a river system, the higher the mortality rates they are likely to suffer due to the associated influx of predators such as herons, otters and cormorants. This influx of predators has the potential to negatively impact wild fish as well, including returning adults.

Another danger of stocking, according to Professor de Leaniz, is the suppression of sexual selection. It has been shown that the survival rates of cod increase dramatically in line with the number of males that were available to their mother during spawning.

Pairing in wild salmon, as with cod, is not random, and mate choice influences their offspring’s ability to fight pathogens and withstand parasites. Consequently, hatchery fish tend to suffer more from disease and parasites than wild fish.

Genetic Dilution

Professor de Leaniz argues that perhaps the greatest danger of artificial stocking to wild salmon stocks is the potential impact on the genetics of locally adapted wild populations. In order to highlight the significance of local adaptation to the survival of salmon stocks, de Leaniz cited a study in which salmon eggs from a Scottish river were reared alongside eggs from a Spanish river, after which the juveniles from both populations were released into the native river of the Spanish fish.

Over a 2 year period, the mean return rate of the “locally adapted” native Spanish fish was 7.85% while the “foreign” Scottish fish only achieved 2.88% returns. Stocking of hatchery-reared fish significantly diminishes selection against mal-adapted phenotypes, potentially leading to the genetic dilution of locally adapted populations when hatchery fish breed with wild fish.

This dilution, it is argued, has the potential to cause significant long-term declines in the survival rates of wild populations. As such, an evolutionary approach to salmon conservation is often recommended, aimed at maintaining the conditions necessary for natural selection to operate most efficiently and unhindered.

The morphological and physiological changes evident in hatchery raised fish in comparison to wild fish were increases in fat deposition which results in deepening of the body amongst hatchery-reared salmonids. This factor highlights the different selective pressures which fish experience in a natural or artificial environment and body shape of wild fish is significantly different with wild fish having a more streamlined shape allowing the wild fish to be more energetically efficient than hatchery reared fish with drag reduced and a lessening of energy used in swimming.

Fry in the wild also displayed darker parr marks than hatchery controls, and this would have made them more cryptic and less conspicuous to predators. The time required by released hatchery fish to change colour to avoid predators was demonstrated to be higher for stocked fish compared to wild fish.

Time in Hatchery - Divergence from Wild Salmon

Juvenile salmon stocked in the wild strongly diverged from hatchery fish with increasing time spent in the wild but did not appear to converge towards the body shape of wild fish, which remained morphologically differentiated from both hatchery controls and stocked fish. This point illustrates that time spent in a hatchery may permanently affect morphology and thus fitness to survive in the wild when compared to wild fish in a natural environment.

The fitness implications of such changes are likely to be adaptive to their environment which may affect swimming ability, feeding ability and predator avoidance.

The presentation demonstrated that hatchery salmon are morphologically different through body shape, forebrain development (Movement), erosion of fins and opercula causing mismatch with natural conditions and lacking predator avoidance skills

Hatchery-reared fish typically perform poorly in the wild and the results of this study indicate that this may be due to phenotypic mismatch, i.e. because hatcheries generate fish that are phenotypically mismatched to the natural environment.

The aspect of helping salmon populations by stocking eyed ova was discussed with Professor Garcia De Leanitz indicating that mate selection process is complex and our choice of mate may not be the fish of choice for the female. It is evident that females may select their mates by a complex series of factors to enhance genetic variability and dissimilarity.

Take Home Message

The take home message from this presentation must be that time spent in a hatchery will negatively affect survival of released fish and will impact negatively on population size. If hatcheries are to be used they must concentrate on releasing fish at earliest time with eyed ova preferred with certain reservations noted in choice of mate.

However the presentation noted that a natural wild system is the preferred option. It is obvious that asymmetry (fin erosion, opercula) in fish, under developed predator avoidance skills and poorly developed brain movement function will affect survival and population diversity and size.

Finally, de Leaniz made the point that over the years hatcheries have been used to mask declining salmon returns, and consequently the underlying ecological causes of these declines have often gone unaddressed.