Sea Migration Research Articles

Risk perception and desire in decision-making: the case of Syrians’ sea migration to Europe

ABSTRACT Based on narrative interviews with Syrian refugees arriving in Europe via the Mediterranean Sea, this study contributes to a deeper understanding of the decision-making processes involved in migration. It explores the interplay between the subjective factors such as risk perception and desire experienced by Syirans who took risky sea crossings. The primary analytical approach involves comparing the judgment of risk in one's own realized migration versus the potential migration of others. Participants who successfully crossed the sea and arrived in Europe considered their decisions valid, yet they would not recommend the same path to others. This contradiction can be explained by the significant role that the desire for a life change played in their decision-making, as it influenced their own risk assessment but was absent in their assessment of risk for others. The study further suggests that decision-making in risky migration is not solely about weighing the risks of staying versus leaving. Rather, it involves evaluating the worth of a desired life transformation against the perceived risks associated with the migratory journey.

Thiamin dynamics during the adult life cycle of Atlantic salmon (Salmo salar).

Thiamin is an essential water-soluble B vitamin known for its wide range of metabolic functions and antioxidant properties. Over the past decades, reproductive failures induced by thiamin deficiency have been observed in several salmonid species worldwide, but it is unclear why this micronutrient deficiency arises. Few studies have compared thiamin concentrations in systems of salmonid populations with or without documented thiamin deficiency. Moreover, it is not well known whether and how thiamin concentration changes during the marine feeding phase and the spawning migration. Therefore, samples of Atlantic salmon (Salmo salar) were collected when actively feeding in the open Baltic Sea, after the sea migration to natal rivers, after river migration, and during the spawning period. To compare populations of Baltic salmon with systems without documented thiamin deficiency, a population of landlocked salmon located in Lake Vänern (Sweden) was sampled as well as salmon from Norwegian rivers draining into the North Atlantic Ocean. Results showed the highest mean thiamin concentrations in Lake Vänern salmon, followed by North Atlantic, and the lowest in Baltic populations. Therefore, salmon in the Baltic Sea seem to be consistently more constrained by thiamin than those in other systems. Condition factor and body length had little to no effect on thiamin concentrations in all systems, suggesting that there is no relation between the body condition of salmon and thiamin deficiency. In our large spatiotemporal comparison of salmon populations, thiamin concentrations declined toward spawning in all studied systems, suggesting that the reduction in thiamin concentration arises as a natural consequence of starvation rather than to be related to thiamin deficiency in the system. These results suggest that factors affecting accumulation during the marine feeding phase are key for understanding the thiamin deficiency in salmonids.

Long-Term Trends in Freshwater and Marine Growth Patterns in Three Sub-Arctic Atlantic Salmon Populations

The rapid warming of the Northern hemisphere has especially challenged the evolvability of anadromous fish species, such as Atlantic salmon (Salmo salar), which must cope with drastically different environments depending on their life-history stage. We studied the long-term trends in, and the effects of environmental factors and life-history traits on, Atlantic salmon growth rates in both freshwater and in the ocean using c. 35,000 scale samples collected across 48 years from spawners returning to three tributaries of the subarctic River Teno in the northernmost parts of Finland and Norway (70° N). The freshwater growth has decreased in all three populations and spending more than three juvenile years in freshwater before the sea migration comes at the expense of growth. On the other hand, returning mature salmon (one-sea-winter, 1SW) showed increased growth at the sea with increasing marine temperatures, which results in larger sizes at return in 1SW spawners. We did not observe such trends in growth rates in larger, two-sea-winter salmon. Here, we report the contrasting responses in Atlantic salmon growth rates to a warming climate depending on the life-history stage.

Relations of coral reef benthos composition and horseshoe crabs’ gut content

Intensive earlier studies on horseshoe crab feeding ecology are focused on the Atlantic species, Limulus polyphemus (Linnaeus, 1758). However, the distribution of species, food abundance, and availability of benthos in a particular environment might influence the horseshoe crab's preference for diet in a particular region. The aims of this research are to analyse the benthos composition in Tachypleus gigas spawning site and coral reefs located near the spawning ground in Cherok Paloh, Pahang, and compare it with the food composition inside the T. gigas digestive track. A total of 30 samples of male and female horseshoe crabs, T. gigas respectively, were harvested by using a fishing net during the incoming high tide. Their guts were dissected, and the contents were analysed according to Squires and Dawe criteria. Results showed that echinoderm was the main food composition in the gut of males (54.27%) and females (51.44%) during the open sea migration phase. Amuk-amuk coral reef (3°41'51"N 103°24'13"E), Raja Muda coral reef (3°38'01"N 103°28'23"E) and Air Leleh coral reef (3°35'38"N 103°29'00"E) are the nearest sea urchin habitats to the sampling area. Benthos analysis showed higher echinoderm composition in those coral reefs (31.58 – 42.11%). There is no echinoderm composition found in the spawning site sediment. Further study is needed to provide reliable data on the significance of coral reefs in the horseshoe crab's foraging ecology.

Empathy, geography and immigration: Political framing of sea migrant arrivals in European media

How is European media framing sensitive to events such as refugee border crossing and irregular migrants’ arrivals? While news outlets adjust the tone around immigration following ideology, do the contextual characteristics of these incidents matter? This article explores two factors that could explain the varying framing of these highly political events in European mainstream media. One explanation focuses on the role of migrants’ conditions, such as migrants’ way of transit and subsequent human sufferance (or lack thereof). Another emphasizes the role of geography, in particular the location of migrants’ territorial identification relative to the receiving communities. Focusing on the case of sea migration and small boat arrivals in Southern Europe, I argue that the emotional triggers determined by migrants’ transit and their geographical point of detection systematically moderate each other, and jointly affect how the media describe these cross-border immigration events. Empirically, the article presents original newspaper data from Greece, Italy and Spain that collates geospatial information on immigrants’ sea transit and the related number of injuries and deaths during transit. Statistical results indicate that media framing is more sympathetic to events involving suffering migrants, but that this positive framing diminishes if migrants are located only at the border of the national territory and disappears if the migrants are identified in more distant, foreign waters. The results suggest nuanced conditions in which migration can be presented by the media aside from their ideological lenses.

Early-season brown trout (Salmo trutta) migrants grow and survive better at sea.

The timing of seaward migration is a key life‐history trait for many anadromous fish species, with growth and survival at sea depending on a match/mismatch scenario between the timing of the sea entry and optimal conditions. Based on a 25‐year study with 15,226 individually tagged brown trout (Salmo trutta) in a Norwegian river, we analysed how the within‐season timing of sea migration impacted growth and survival. In both first‐time and veteran migrants, marine growth was highest for early migrating individuals, large individuals, and those with a low condition factor when entering the sea. Survival was highest for individuals entering the sea early in the season. In first‐time migrants, survival increased with body length. Survival also increased with the number of other smolts migrating simultaneously. As the early smolts were the most successful, it may seem strange that many smolts migrate later in the season. We suggest that late‐migrating smolts may not be of a size and/or physiological state suitable for early marine conditions, and may make the best of a bad situation.

Saving migrants’ lives at sea: Improving search and rescue operations

The present study focuses on the Mediterranean Sea migration crisis and investigates the effectiveness of search and rescue (SAR) operations alongside measures to reduce the number of deaths of migrants at sea. It also describes the stakeholders involved in SAR activities. The paper first analyzes secondary data and the results of 24 in‐depth interviews in order to develop an analytical framework, which is then complemented by a system dynamics model to explore the complexity and interactions among stakeholders in SAR operations. The study shows that the death toll at sea can be reduced by enhancing cooperation among stakeholders by providing legal migration pathways under certain conditions and by engaging in more effective migrant detection and interception at sea. Lastly, raising potential migrants’ awareness about the risk of death during the sea crossing should be seen as an additional measure, while SAR activities should be maintained to prevent loss of life at sea.

Escalating the conflict? Intersex genetic correlations influence adaptation to environmental change in facultatively migratory populations.

Males and females are often subject to different and even opposing selection pressures. When a given trait has a shared genetic basis between the sexes, sexual conflict (antagonism) can arise. This can result in significant individual‐level fitness consequences that might also affect population performance, whilst anthropogenic environmental change can further exacerbate maladaptation in one or both sexes driven by sexual antagonism. Here, we develop a genetically explicit eco‐evolutionary model using an agent‐based framework to explore how a population of a facultatively migratory fish species (brown trout Salmo trutta) adapts to environmental change across a range of intersex genetic correlations for migration propensity, which influence the magnitude of sexual conflict. Our modelled focal trait represents a condition threshold governing whether individuals adopt a resident or anadromous (sea migration) tactic. Anadromy affords potential size‐mediated reproductive advantages to both males and females due to improved feeding opportunities at sea, but these can be undermined by high background marine mortality and survival/growth costs imposed by marine parasites (sea lice). We show that migration tactic frequency for a given set of environmental conditions is strongly influenced by the intersex genetic correlation, such that one sex can be dragged off its optimum more than the other. When this occurred in females in our model, population productivity was substantially reduced, but eco‐evolutionary outcomes were altered by allowing for sneaking behaviour in males. We discuss real‐world implications of our work given that anadromous salmonids are regularly challenged by sea lice infestations, which might act synergistically with other stressors such as climate change or fishing that impact marine performance, driving populations towards residency and potentially reduced resilience.

An opinion piece: the evolutionary and ecological consequences of changing selection pressures on marine migration in Atlantic salmon.

There are strong signals that the selection forces favouring the expression of long‐distance sea migration by Atlantic salmon (Salmo salar) are changing. Unlike many other behavioural traits, the costs of migration are incurred before any fitness benefits become apparent to the migrant. The expression of this behaviour has thus been shaped by selection forces over multiple generations and cannot respond to short interval (within a single generation) environmental change as many other behavioural traits can. Here we provide a framework to examine the evolutionary and ecological consequences of a sustained increase in migration cost. We argue that Atlantic salmon may have entered an evolutionary trap, where long‐distance sea migration has become maladaptive because of shifting environmental conditions. We predict that if higher migration costs (affecting survivorship and ultimately fitness) persist, then shifting selection pressures will result in continuing declines in population size. We suggest, however, that in some populations there is demonstrable capacity for evolutionary rescue responses within the species which is to be found in the variation in the expression of migration. Under a scenario of low to moderate change in the selection forces that previously promoted migration, we argue that disruptive, sex‐based selection would result in partial migration, where females retain sea migration but with anadromy loss predominantly in males. With more acute selection forces, anadromy may be strongly selected against, under these conditions both sexes may become freshwater resident. We suggest that as the migration costs appear to be higher in catchments with standing waters, then this outcome is more likely in such systems. We also speculate that as a result of the genetic structuring in this species, not all populations may have the capacity to respond adequately to change. The consequences of this for the species and its management are discussed.

Evidence of long-distance coastal sea migration of Atlantic salmon, Salmo salar, smolts from northwest England (River Derwent)

BackgroundCombining data from multiple acoustic telemetry studies has revealed that west coast England Atlantic salmon (Salmo salar L.) smolts used a northward migration pathway through the Irish Sea to reach their feeding grounds. Hundred Atlantic salmon smolts were captured and tagged in May 2020 in the River Derwent, northwest England as part of an Environment Agency/Natural England funded project.ResultsThree tagged smolts were detected on marine acoustic receivers distributed across two separate arrays from different projects in the Irish Sea. One fish had migrated approximately 262 km in 10 days from the river mouth at Workington Harbour, Cumbria to the northernmost receiver array operated by the SeaMonitor project; this is the longest tracked marine migration of an Atlantic salmon smolt migrating from the United Kingdom. This migrating fish displayed behaviours which resulted in fast northward migration. The remaining two fish were detected on a receiver array operated by a third project: the Collaborative Oceanography and Monitoring for Protected Areas and Species (COMPASS).ConclusionThese detections further provide evidence that migration to reach marine feeding grounds of at least a proportion of salmon smolts from rivers draining into the Irish Sea is northerly, though without a southern marine array it is impossible to conclude that this is the only route. The pattern of these detections would not have been possible without the collaborative efforts of three distinct and separately funded projects to share data. Further work is required to fully understand migration trajectories in this species on the west coast of the British Isles.

Defying Davy Jones: The Impact of Maritime Search and Rescue Operations on Irregular Migration in the Central Mediterranean

Davy Jones' Locker is well known in legend as being the resting place for those lost at sea, but even more noteworthy is the longstanding tendency of seafarers to defy Davy Jones and seek to rescue those in distress. Rescuing migrants at sea is fraught with controversy, which is especially evident in the ongoing issue of migration in the Mediterranean. So problematic did the issue of migrant deaths in the Mediterranean become, that search and rescue (SAR) operations were organised to address the crisis. This came with its own political backlash, with SAR operations being criticised by states as creating an incentive for migration. Such research is especially critical for Ireland in the deployment of Irish naval forces to conduct SAR in the Central Mediterranean and the importance of an informed analysis to determine such a vital aspect of contemporary European security and humanitarianism. This article studies maritime SAR operations in an attempt to deduce whether they incentivise irregular sea migration in the Central Mediterranean Route. Utilising numbers of migrant arrivals and deaths, contrasted with the nature of various SAR operations against which the migration occurred, this article demonstrates that there is no correlation between migrant numbers and proactive SAR operations. This article aims to provide clarification on the controversial subject of maritime SAR and demonstrate that conducting such operations does not lead to an increase in irregular migration.

Combining acoustic telemetry with a mechanistic model to investigate characteristics unique to successful Atlantic salmon smolt migrants through a standing body of water

The Atlantic salmon, Salmo salar Linnaeus 1758, is a charismatic, anadromous species that has faced dramatic declines throughout its range. There is currently a lack of information on the effect of free-standing bodies of water on a key life event, sea migration, for the species. This study extends our understanding in this area by combining acoustic telemetry with a correlated random walk model to try to examine potential morphological and behavioural factors that differentiate successful from unsuccessful migrants through Scotland’s largest lake. Consistent with other studies, we found that smolts experienced a high rate of mortality in the lake (~ 43%), with approximately 14% potentially predated upon by birds and 4% by Northern pike. Migration speed in the lake was slow (the mean minimum movement speed between centres of activity was 0.13 m/s), and pathways frequently deviated away from the outlet river. There was no evidence of a morphological or behavioural trait or migratory pathway that distinguished successful from unsuccessful smolts. This suggests that migration movement direction in the main body of Loch Lomond appeared to be random. This was further supported by the output of a correlated random walk model which closely resembled the pathway and migration speed and distance patterns displayed by successful migrants. However, once successful smolts came within ~2 km of the lake exit, a high proportion remained in this region prior to entering the River Leven. We suggest that this “goldilocks zone” is where directional cues become apparent to migrating fish. Future studies should combine random walk models with environmental variables to determine if external factors are driving the apparently random movement patterns exhibited by smolts in lakes.

Anadromous red-spotted masu salmon (Oncorhynchus masou ishikawae), a southernmost sea-migration form of salmonid, displays low variation in both age at seaward migration and sea age.

We examined variations in age at seaward migration and sea age for the anadromous form of red-spotted masu salmon (Oncorhynchus masou ishikawae) in two Japanese rivers. The anadromous form of red-spotted masu salmon expressed only two sea migration patterns in the two rivers: (a) the majority of the salmon (95%, n=81) were of age-0, and age-1 migrants were rare (n=4); and (b) all the salmon examined (n=22) made a return migration within a year, with 23% of the salmon exhibiting potamodromy in the river. Owing to low variation in their sea migratory patterns, the anadromous form of red-spotted masu salmon is likely vulnerable to environmental fluctuations.

Sex-specific lipid profiles in the muscle of Atlantic salmon juveniles

Energy allocation in juvenile fish can have important implications for future life-history progression. Inherited and environmental factors determine when and where individuals allocate energy, and timely and sufficient energy reserves are crucial for reaching key life stages involved in the timing of maturation and sea migration. In Atlantic salmon, lipid reserves are predominantly found in the viscera and myosepta in the muscle and have been shown to play a key role in determining the timing of maturity. This life-history trait is tightly linked to fitness in many species and can be different between males and females, however, the details of relative energy allocation in juveniles of different sexes is not well understood. Therefore, the aim of this study was to investigate the effects of sex, genetics and environment during juvenile development of salmon on the amount and composition of their lipid reserves. To do so, juvenile salmon were fed one of two different lipid food contents during their first summer and autumn under common-garden conditions. Muscle lipid composition and concentrations were determined by thin layer chromatography. The muscle lipid class concentrations covaried negatively with body length and males showed higher concentrations than females for phosphatidylcholine, cholesterol, sphingomyelin, and triacylglycerol. This sex-specific difference in major lipid classes presents a new scope for understanding the regulation of lipids during juvenile development and gives direction for understanding how lipids may interact and influence major life-history traits in Atlantic salmon.

Changes in growth and migration patterns of sea trout before and after the introduction of Atlantic salmon farming

Abstract Marine growth has strong implications for reproductive potential and ultimate fitness of sea trout. Hence, the effects of anthropogenic factors on marine growth are important when evaluating population responses and implementing management measures. Temporal changes in growth patterns of sea trout from three Norwegian and two Irish watercourses were examined, covering time spans of 25–65 years. Elemental chemistry Ba:Ca profiles and visual reading of fish scales were used to estimate smolt length and lifetime growth after first sea entry. Reduced growth after the first sea entry coincided with periods of nearby (<14 km) salmon-farming activity in impacted watersheds in both countries. Increased Ba:Ca levels were also recorded during these periods, likely indicating reduced residency in marine habitats caused by premature return to freshwater and estuaries. An increase in estimated length at first sea entry coinciding with salmon-farming activity, for groups of fish sampled after sea migration, suggests a size-selective marine mortality, with the smallest individuals experiencing a larger mortality.

PRELIMINARY RESEARCH ON THE SURVIVAL STRATEGIES AMONG PALA’O PEOPLE IN BANGGI ISLAND

This paper is based on a preliminary study of the survival of Pala’o ethnic group living in Banggi Island located in the northern part of Sabah, Malaysia. Banggi Island is inhabited by various ethnic groups and dominated by Bajau Ubian, Dusun Bonggi, Suluk, Kegayan, Bajau Sama’ and Molbog ethnic groups. Today, Banggi Island is also inhabited by the ethnic of Pala’o, also known as Bajau Laut or sea gypsies, and Palauh/Sama Dilaut, which originate in the Semporna waters of the Sulu and Celebes Sea. Based on the qualitative approach through in-depth interviews, the Sea Gypsies off the coast of Karakit town, Banggi Island was found to be able to adapt to changes in the environment and adapt it to their suitability. The need to continue living is seen as an essential part of this ethnic 'migration'. The study found that for survival, the Pala'o tribe in the context of this study adopted four survival strategies namely sea migration to land, physical strategy, social strategy and economic strategy. However, the fate of Pala'o's ethnic group remained largely unchanged. They are still subject to poverty and they have always been, and still remain, ethnic 'without citizenship'. The success of a survival strategy is seen to be closely related to the economic sector and the work it does, knowledge, skills and education but it does not apply to this Pala'o tribe. Their lives are still being faced by the hardships of the poor but their insistence on life has given them a chance to continue living even though their lives on the land are different from their life's experiences in the great sea.

Timing is everything: Survival of Atlantic salmon Salmo salar postsmolts during events of high salmon lice densities

Abstract Atlantic salmon in aquaculture act as reservoir hosts and vectors of parasites like salmon lice and this parasite is shown to harm wild salmonid populations. In this study, n = 29,817 tagged Atlantic salmon were studied in four release trials. Half of the released fish were given prophylactic treatment against lice, the other half represented sham control fish. We used a nested design comparing years with low and high lice density and seasonal dynamics in infestation pressure. The released Atlantic salmon thus experienced highly variable lice infestation pressures, which we linked to survival and growth in returning fish. The fish were released in a protected ‘National Salmon Fjord’ and n = 559 Atlantic salmon were recaptured after spending 1–4 years at sea. In most experimental groups 1%–2.5% of the fish were recaptured at return. However, survival of unprotected fish was extremely low for the trial released at the highest density of lice: only 0.03% of these Atlantic salmon returned to the river, compared to 1.86% in the protected group. Synthesis and applications. We document that high lice density can cause more than 50 times higher mortality risk in Atlantic salmon on their sea migration, even in a fjord with protected status. Fine‐tuned and hard‐to‐predict year‐to‐year differences in timing, both for the wild smolt migration and the population build‐up of lice released from aquaculture, means life or death to wild salmon. Management actions such as spatial segregation of farmed fish and lice (e.g. closed farm pens), and/or moving farms away from vulnerable habitats for wild salmonids (fjords and coastal areas), may be needed to ensure sustainable coexistence of wild and farmed Atlantic salmon.

Food and temperature stressors have opposing effects in determining flexible migration decisions in brown trout (Salmo trutta).

With rapid global change, organisms in natural systems are exposed to a multitude of stressors that likely co-occur, with uncertain impacts. We explored individual and cumulative effects of co-occurring environmental stressors on the striking, yet poorly understood, phenomenon of facultative migration. We reared offspring of a brown trout population that naturally demonstrates facultative anadromy (sea migration), under different environmental stressor treatments and measured life history responses in terms of migratory tactics and freshwater maturation rates. Juvenile fish were exposed to reduced food availability, temperatures elevated to 1.8°C above natural conditions or both treatments in combination over 18months of experimental tank rearing. When considered in isolation, reduced food had negative effects on the size, mass and condition of fish across the experiment. We detected variable effects of warm temperatures (negative effects on size and mass, but positive effect on lipids). When combined with food restriction, temperature effects on these traits were less pronounced, implying antagonistic stressor effects on morphological traits. Stressors combined additively, but had opposing effects on life history tactics: migration increased and maturation rates decreased under low food conditions, whereas the opposite occurred in the warm temperature treatment. Not all fish had expressed maturation or migration tactics by the end of the study, and the frequency of these 'unassigned' fish was higher in food deprivation treatments, but lower in warm treatments. Fish showing migration tactics were smaller and in poorer condition than fish showing maturation tactics, but were similar in size to unassigned fish. We further detected effects of food restriction on hypo-osmoregulatory function of migrants that may influence the fitness benefits of the migratory tactic at sea. We also highlight that responses to multiple stressors may vary depending on the response considered. Collectively, our results indicate contrasting effects of environmental stressors on life history trajectories in a facultatively migratory species.

The cost of anadromy: marine and freshwater mortality rates in anadromous Arctic char and brown trout in the Arctic region of Norway

It is hypothesized that in diadromous fish, migrations may occur because of differences in the availability of food in marine and freshwater habitats. The benefits of migration to sea may be increased growth opportunities and reproductive output, while the costs may be increased mortality and increased energy use. Here we examine mortality rates of anadromous Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) in fresh water and at sea over a 25-year period to test these hypotheses. Daily mortality rates were 5–15 times higher at sea than in fresh water, with highest rates for first-time migrants, inferring a clear trade-off between increased mass gain and mortality risk during the sea migration. Descending smolts were caught in a trap at the outlet of the river, individually tagged, and thereafter recorded each time they passed through the trap on their annual migration between the river and the sea. Brown trout females seemed to benefit to a higher degree from migrating to sea than did female Arctic char, probably because of the higher growth rate at sea, and hence higher reproductive output.

Smugglers, migrants, and demons

ABSTRACTHaitian sea migration and US maritime policing have emerged in tandem since the 1980s. During this time, many Haitians have begun to assume that migration voyages succeed only because of ritual exchanges—in particular, transactions between migrants and sea‐traversing, other‐than‐human beings. These ritual payments, along with other activities of border crossing and control, have placed ships, routes, and offshore detention centers in an interconnected constellation that spans the northern Caribbean. These cosmographically deep spatial configurations exceed concepts like “region” or “sociocultural area.” Cosmographic depth, while not unique to these spaces, is made visible in the array of entities, forces, and moral sensibilities that compose them. Seeing cosmographically highlights this depth, which is often rendered inconsequential by dominant bureaucratic registers of border securitization. [oceans, migration, space, ritual economies, cosmology, Guantánamo Bay, Haiti, Caribbean]