Animal Behaviour in Salmon Conservation

Hatcheries play a crucial role in salmon conservation, particularly in regions like the Great Lakes, where the natural salmon population has been considerably diminished due to overfishing, habitat destruction, and pollution. Since the 1960s, hatchery-raised fish have been introduced to supplement the dwindling populations and support both ecological balance and fishing industries. However, existing hatchery practices often fail to effectively mimic the complex and nuanced conditions of natural environments and behaviors, which can lead to less viable populations in the long term. Key deficiencies in hatchery practices include:

• Lack of mimicry for natural settings: Hatchery rearing environments often lack the diversity of habitats found in natural ecosystems, which are essential for the fish to learn and develop adaptive behaviors crucial for survival.

• Inability to account for wild behavior: Many hatchery protocols do not adequately replicate the social structures and interactions observed in wild salmon, potentially impairing the development of necessary survival strategies among fish raised in these environments.

• Restriction on mate choice among salmon: Hatchery environments can severely limit or eliminate the ability of salmon to choose partners, disrupting natural selection processes that favor stronger mating pairs.

• Absence of polyandry (multiple mating) strategies: Hatcheries often overlook female salmon's natural propensity for polyandry, leading to a reduction in the genetic diversity that benefits population resilience.

• Ignoring alternative reproductive tactics (ARTs): Different male salmon adopt various strategies for reproduction, such as sneaking or guarding, which are often inadequately represented in hatchery breeding programs.

These factors considerably influence genetic diversity and the overall health of salmon populations, making it imperative for hatcheries to revise their methodologies to align more closely with natural reproductive and developmental processes.

Salmon Reproductive Tactics

Different male salmon employ various reproductive strategies which can be categorized primarily into two alternative reproductive tactics (ARTs):

1. Sneaker ("Jack"): Smaller males, often referred to as jacks, who typically attempt to spawn quickly and covertly, avoiding larger males and territorial disputes. Their reproductive success is contingent on stealth and opportunism.

2. Guard ("Hooknose"): Larger, dominant males known as hooknose defend breeding territories vigorously, ensuring they mate with multiple females and securing their genetic legacy. They are characterized by physical features that help them perform effectively in defending their territory.

Mating Behavior

Notably, female salmon exhibit a behavior called polyandry, wherein they mate with multiple males. Approximately 60% of these matings involve between 2 to 5 males, with jacks often included. This behavior is driven by female preferences for larger males, as well as those exhibiting diversity in their immune gene compatibility, inferred from MHC (Major Histocompatibility Complex) diversity. The genetic variation introduced through multiple mating ventures is essential for the health of future generations.

External Fertilization

This reproductive strategy facilitates manipulation of offspring development and improved survival outcomes. It allows for broader genetic mixing and can enhance the vitality of hatchery-raised offspring by ensuring a more robust genetic foundation.

Genetic Research and MHC

Studies have utilized genetic sampling from spawning salmon in wild populations to evaluate:

• Microsatellite and MHC diversity: These studies reveal how reproductive tactics influence genetic variation and can inform selection strategies in hatcheries.

• Comparative analysis between males from different ARTs: Research has shown that the Major Histocompatibility Complex (MHC) plays a crucial role in immune response, with specific alleles exhibiting variable frequencies between hooknose and jack males. Genotyping has revealed that heterozygosity and allelic diversity correlates positively with reproductive success and offspring viability, illustrating the genetic complexities of salmon populations.

• MHC Class I and Class II

  • Class I (MHC I-α1): Vital for viral detection, it has been sequenced in various salmon populations to evaluate allelic diversity, emphasizing the importance of genetic variation in resilience to diseases.

  • Class II (MHC II-ß1): Engages in the detection of bacterial infections, showing significant variation in allele frequencies among different reproductive strategies. Both classes of MHC are critical for the salmon's ability to mount effective immune responses, which can considerably affect reproductive success and overall population health.

Research Findings

Analysis of hatching success rates highlights the importance of genetic diversity facilitated through female polyandry:

• Hatching Success Rates: Studies have shown significantly higher hatching success rates in polyandrous matings, indicating a hidden reservoir of immune gene diversity that may be pivotal for future population resilience. This emphasizes the necessity of incorporating practices that mirror natural breeding behaviors in hatchery operations.

• ART Differences: Genetic variations have been noted among sexes and their respective ARTs, specifically in terms of MHC allelic distributions, suggesting complex underlying genetic and evolutionary dynamics that are vital for understanding population health.

Conclusions

This research highlights the necessity for hatchery operations to adapt methods that truly reflect the natural behaviors of salmon while emphasizing the importance of genetic diversity. Recognizing the differences in reproductive tactics and genetic makeup among salmon populations can inform more effective conservation strategies that enhance population viability in both hatchery and wild environments. The findings underscore the need for implementing approaches that mimic natural selection pressures, particularly considering male mating strategies and the significant impact of female choice on genetic health in salmon populations.