Challenges for Diadromous Fishes in a Dynamic Global Environment

<em>Abstract</em>.-Pacific salmon <em>Oncorhynchus </em>spp. catches are at historic high levels. It is significant that one of the world's major fisheries for a group of species that dominates the surface waters of the subarctic Pacific is actually very healthy. Natural trends in climate are now recognized to cause large fluctuations in Pacific salmon production, as shown in historical records of catch and recent changes probably have been affected by greenhouse gas induced climate changes. Pink salmon <em>O. gorbuscha </em>and chum salmon <em>O. keta </em>production and catch has increased in the past 30 years and may continue in a similar trend for for the next few decades. Coho salmon <em>O. kisutch </em>and Chinook salmon <em>O. tshawytscha </em>catches have been declining for several decades, particularly at the southern end of their range, and they may continue to decline. In the 1970s, hatcheries were considered to be a method of adding to the wild production of coho and Chinook salmon because the ocean capacity to produce these species was assumed to be underutilized. Large-scale changes in Pacific salmon abundances are linked to changes in large-scale atmospheric processes. These large-scale atmospheric processes are also linked to planetary energy transfers, and there is a decadal scale pattern to these relationships. Pacific salmon production in general is higher in decades of intense Aleutian lows than in periods of weak Aleutian lows. Key to understanding the impact of climate change on Pacific salmon is understanding how the Aleutian low will change. Chinook and coho salmon are minor species in the total commercial catch, but important socially and economically in North America. A wise use of hatcheries may be needed to maintain abundances of these species in future decades.

Challenges for Diadromous Fishes in a Dynamic Global Environment

<em>Abstract</em>.-Declines in recruitment of temperate anguillid eels have occurred in the past 30 years in many areas of their species ranges. The cumulative effects of anthropogenic changes to their freshwater growth habitats are likely contributors to reductions in population sizes, but changes in ocean-atmospheric conditions in the ocean also appear to be contributing to the declines. This paper reviews how changes in the ocean may contribute to recruitment declines by affecting the spawning location of silver eels, larval feeding success, or the transport of their leptocephalus larvae by ocean currents. Recruitment of European eels <em>Anguilla anguillla </em>has shown correlations with the North Atlantic Oscillation and specific changes in ocean conditions in the Sargasso Sea where spawning and development occurs. The American eel <em>A. rostrata </em>spawns in an area that overlaps with the European eel and so could also be affected by these types of changes. Recruitment of Japanese eels <em>A. japonica </em>appears to be correlated to the El Niño Southern Oscillation index and latitudinal changes in salinity fronts in the western North Pacific. The general spawning and recruitment patterns of the temperate Australasian shortfin eels <em>A. australis </em>and New Zealand longfin eels <em>A. dieffenbachii </em>in the western South Pacific are similar to those of the northern temperate anguillids and also may be affected by El Niño-related factors. The changes in ocean conditions associated with atmospheric forcing or a warming of the ocean could alter the biological characteristics of the surface layer where leptocephali feed, due to changes in productivity or community structure, in addition to having possible effects on larval transport and location of the spawning areas by silver eels. Changes in ocean-atmospheric conditions could result in lower feeding success and survival of leptocephali, or increased retention in offshore areas due to changes in the location of spawning areas, resulting in reductions in recruitment.

Challenges for Diadromous Fishes in a Dynamic Global Environment

<em>Abstract</em>.-Climate change can have an effect on species distributions. The 1900 distribution and potential future distribution of diadromous fish in Europe, North Africa, and the Middle East were explored using generalized additive models (GAMs) and selected habitat characteristics of 196 basins. Robust presence-absence models were built for 20 of the 28 diadromous species in the study area using longitude, annual temperature, drainage surface area, annual precipitation, and source elevation as explanatory variables. Inspection of the relationship between each variable and species presence-absence revealed that the GAMs were generally interpretable and plausible. Given the predicted rise in annual temperature in climate models ranging between 1°C and 7°C by 2100, the fish species were classified according to those losing suitable basins, those gaining suitable basins, and those showing little or no change. It was found that the climate envelopes based on temperature and precipitation for diadromous species would, in general, be shifted farther northeastwards by 2100, and these shifting ranges were comparable with those assessed in other studies. The uncertain future of some species was highlighted, and it was concluded that conservation policy and management plans will need to be revised in the face of climate change.

Challenges for Diadromous Fishes in a Dynamic Global Environment

<em>Abstract</em>.-In this paper, we develop logistic stream temperature models for 17 selected sites in northeastern North America and evaluate the potential changes from warming climate under two scenarios (low and medium-high emissions). Classification of the magnitude of the (1) long-term (1980-2002) and (2) annual thermal regimes allowed examination of the relative spatial and temporal patterns of instream thermal variability across the 17 sites. At the regional scale, the classification identified three broad groups of rivers (cool, intermediate, and warm) reflecting geographical location and moderated by site-specific factors. The interannual classification identified four thermal year types reflecting increasing magnitude and variability in the annual thermal regime. The dominance of thermal year types and the frequency of occurrence indicated significant variability between years for all sites and within thermal regions. Under the two climate change scenarios, stream temperatures in the 17 sites are projected to increase by 2050. However, there are regional differences with intermediate and warm region rivers projected to be more affected, particularly under the medium-high emissions scenario. More significantly, the duration of weeks when temperatures exceed 20°C (taken as a threshold of thermal stress for Atlantic salmon <em>Salmo salar</em>) is projected to increase with variability in response between river groups. We comment on the ecological significance of these potential future increases in stream temperature and duration for Atlantic salmon in the region.

Challenges for Diadromous Fishes in a Dynamic Global Environment

<em>Abstract</em>.-Tagging fish with electronic tags can provide information on movement, migration, behavior, and stock structure while diadromous species are at sea. The state of the art technology for tracking fishes in the marine environment includes two families of tags. Archival tags store data and either relay them to satellites or require recapture for interrogation. Low return rates for diadromous species make these tags very expensive to use. A second type, acoustic tags, sends signals to passive receivers. Information is collected from the fish only when it is within range of a receiver. Technology is now being developed to mesh these tags into a fully integrated tag that will permit archived data to be transmitted acoustically over multiple frequencies to receivers allowing data retrieval without recapturing the animal. The new technology includes a "business card" tag that is a miniaturized receiver coupled with a coded pulse transmitter. These tags will exchange and record individual-specific codes when two animals carrying them come within acoustic range of each other, which will allow data from many animals to be moved ashore through few animals. These devices would be ideal for quantifying the degree of school fidelity (or, conversely, mixing) or the degree of at sea interaction of fishes from different river systems and provide ecological information to enhance management in an ecosystem approach to fisheries.

Challenges for Diadromous Fishes in a Dynamic Global Environment

<em>Abstract</em>.-In the study of species life histories and the structure of diadromous populations, an emerging trend is the prevalence of life cycle diversity-that is, individuals within populations that do not conform to a single life cycle pattern. A rapid rise in publications documenting within-population variability in life cycles has resulted in the use of numerous terms and phrases. We argue that myriad terms specific to taxa, ecosystem types, and applications are in fact describing the same phenomenon-life cycle diversity. This phenomenon has been obscured by the use of multiple terms across applications, but also by the overuse of typologies (i.e., anadromy, catadromy) that fail to convey the extent of life cycle variations that underlay population, metapopulation, and species dynamics. To illustrate this, we review migration and habitat-use terms that have been used to describe life cycles and life cycle variation. Using a citation index (Cambridge Scientific Abstracts © Aquatic Sciences and Fisheries Abstracts), terms were tallied across taxonomic family, ecosystem, type of application, analytical approach, and country of study. Studies on life cycle diversity have increased threefold during the past 15 years, with a total of 336 papers identified in this review. Most of the 40 terms we identified described either sedentary or migratory lifetime behaviors. The sedentary-migratory dichotomy fits well with the phenomenon of partial migration, which has been commonly reported for birds and Salmonidae and is postulated to be the result of early life thresholds (switch-points). On the other hand, the lexicon supports alternate modes of migration, beyond the simple sedentary-migratory dichotomy. Here more elaborate causal mechanisms such as the entrainment hypothesis may have application. Diversity of life cycles in fish populations, whether due to partial migration, entrainment, or other mechanisms, is increasingly recognized as having the effect of offsetting environmental stochasticity and contributing to long-term persistence.

Challenges for Diadromous Fishes in a Dynamic Global Environment

<em>Abstract</em>.-Aboriginal people developed integrated ecosystem-based management long before European contact in the 1750s. Ecosystem knowledge contributed the lion's share of precontact wealth. Fisheries drove the early British Columbia economy, but now account for less than 0.5% of gross domestic product. Even thought West Coast research shows that precontact ecosystems could sustain many times current catch value, this still would not weigh heavily against other economic sectors. Single species management has failed to avert the depletion of many fisheries; hence, we now hear calls for ecosystem-based management as opposed to integrated management (used in reference to managing multiple sectors such as fisheries, farmed salmon, oil, and gas, as well as climate change). We suggest that reintegrating ecosystem-based and integrated management necessitates the cooperation of other ocean sectors in generating the information necessary to monitor and restore ecosystems while ensuring that their own operations are sustainable. Currently, there are a number of scientific initiatives, ocean and biological observing platforms, and high-powered models to help develop new management regimes. We consider how this new technology could help to understand the collapse of eulachon <em>Thaleichthys pacificus</em>. Eulachon are of great importance to Native peoples but could well be described as the forgotten anadromous fish of the research community. It is important that both industry and governments recognize the importance of maintaining the long-term viability of these important tools and invest appropriately to ensure sound ecosystem management practices into the future.

Challenges for Diadromous Fishes in a Dynamic Global Environment

<em>Abstract</em>.-The general acceptance that individual fisheries should be managed in the context of the ecosystem of which the target species are a part has led to the paradigm of ecosystem- based fisheries management (EBFM). Such management may be particularly suitable for diadromous fishes, which spend time in rivers, estuaries, and the sea, because their sustainability would benefit from a holistic approach. The extent to which this is possible and has been successful depends on a wide variety of biological, socioeconomic, and political factors. Fishing in all its forms is only one of a broad array of human activities in rivers, estuaries, and the coastal zone; hence, diadromous fisheries management requires not only integration across ecosystems, but also its inclusion in overall planning processes. Tropical diadromous fisheries in developing countries suffer from overfishing, lack of adequate human resources to manage the fisheries, insufficient scientific data for sound management and decision making, lack of monitoring capabilities, poor enforcement of laws, inefficient administration, and increasing conflicts between different types of users. Even in developed countries, many of these issues also have not been addressed. The extent to which an EBFM approach has been successful for tropical diadromous species is discussed using the various barramundi <em>Lates calcarifer</em>, mullet (Mugilidae), and tropical shad (<em>Tenualosa</em>) fisheries of Asia and Australia, taking into account issues of food security and the role of community-based management.

Challenges for Diadromous Fishes in a Dynamic Global Environment

<em>Abstract</em>.-Wild low bush blueberries, advertised as "nature's #1 antioxidant super fruit," require about 2.5 cm of water per 0.4 ha each week during late June and all of July when fruit is forming and maturing. To reduce annual variation in production, Maine's blueberry growers began rapidly expanding the acreage under irrigation in the 1990s. As a result of increased acreage and irrigation, average annual Maine blueberry production increased from 15.8 million kilograms in the 1980s to 32.1 million kilograms in 2006. Endangered Atlantic salmon <em>Salmo salar </em>inhabit the rivers and streams in the watersheds where blueberries are grown. Initially all irrigation water was drawn from surface sources and some withdrawals directly degraded salmon habitat. To address this concern, the Maine State Planning Office coordinated a collaborative planning process that included hydrologists, fisheries biologists, and agricultural scientists from state and federal agencies, nongovernmental organizations, and industry, as well as members of the public and industry management. Following this effort, the large growers within Atlantic salmon watersheds shifted irrigation sources to storage impoundments and groundwater. The process also helped moved the blueberry industry to acknowledge fish habitat as a legitimate competing water use, thus potentially setting the stage for their future acceptance of the concept that there are hydrologic and ecological limits on water use in Atlantic salmon watersheds.

Challenges for Diadromous Fishes in a Dynamic Global Environment

<em>Abstract</em>.-Diadromy is a life history attribute in a small number of fish species, and also some decapod crustaceans and gastropod mollusks, involving regular migrations at defined life history stages between freshwaters and the sea. Despite the relatively few species known to be diadromous, these are often of high fisheries importance owing in part to their migratory movements being spatially and temporally concentrated, making them vulnerable to exploitation. These migrations have important implications for a diverse array of aspects of biology: evolutionary, genetic, biogeographical, ecological, community, and conservation. There are also implications for the acclimatization of species into novel habitats, and deriving from these implications, diadromous fishes introduced into natural ecosystems may have seriously adverse impacts on the receiving ecosystems. As well, diadromy provides some species with the capacity to facilitate restoration of populations caused by adverse impacts on aquatic ecosystems across a broad range of spatial and temporal scales, from the effects of volcanism and glaciation to those of polluting discharges with anthropogenic sources. Allied with these questions is that relating to the importance of habitat connectivity and the vulnerability of diadromous species to events that interfere with up- and downstream migrations in fluvial ecosystems.