Growth in marine mammals: a review of growth patterns, composition and energy investment

Abstract

Growth of structural mass and energy reserves influences individual survival, reproductive success, population and species life history. Metrics of structural growth and energy storage of individuals are often used to assess population health and reproductive potential, which can inform conservation. However, the energetic costs of tissue deposition for structural growth and energy stores and their prioritization within bioenergetic budgets are poorly documented. This is particularly true across marine mammal species as resources are accumulated at sea, limiting the ability to measure energy allocation and prioritization. We reviewed the literature on marine mammal growth to summarize growth patterns, explore their tissue compositions, assess the energetic costs of depositing these tissues and explore the tradeoffs associated with growth. Generally, marine mammals exhibit logarithmic growth. This means that the energetic costs related to growth and tissue deposition are high for early postnatal animals, but small compared to the total energy budget as animals get older. Growth patterns can also change in response to resource availability, habitat and other energy demands, such that they can serve as an indicator of individual and population health. Composition of tissues remained consistent with respect to protein and water content across species; however, there was a high degree of variability in the lipid content of both muscle (0.1–74.3%) and blubber (0.4–97.9%) due to the use of lipids as energy storage. We found that relatively few well-studied species dominate the literature, leaving data gaps for entire taxa, such as beaked whales. The purpose of this review was to identify such gaps, to inform future research priorities and to improve our understanding of how marine mammals grow and the associated energetic costs.

Decreasing body size is associated with reduced calving probability in critically endangered North Atlantic right whales

“…able to capture most of the inter-individual variation in fecundity and explain the decline in calving probability over the last five decades [25]. Therefore, the reduction in length exacerbates the progressive deterioration in right whale health detected in our model and prevents females from reproducing more successfully even when their relative health is good because of lower absolute energy reserves [25], supporting the predictions from marine mammal bioenergetic models [12,13].…”

“…The decreasing trend in individual asymptotic length [ 16 ] was able to capture most of the inter-individual variation in fecundity and explain the decline in calving probability over the last five decades [ 25 ]. Therefore, the reduction in length exacerbates the progressive deterioration in right whale health detected in our model and prevents females from reproducing more successfully even when their relative health is good because of lower absolute energy reserves [ 25 ], supporting the predictions from marine mammal bioenergetic models [ 12 , 13 ]. Age and experience could also play a role in the observed decline, although preliminary investigations do not support this hypothesis (electronic supplementary material).…”

“…whaling [ 9 ]). Bioenergetic models posit that absolute body size contributes to the success of a reproductive attempt [ 12 , 13 ], because larger females can carry more energy to invest in the calf and to buffer against environmental variation during reproduction (e.g. [ 14 , 15 ]).…”

Modeling individual growth reveals decreasing gray whale body length and correlations with ocean climate indices at multiple scales

“…These consequences are particularly true for a capital breeding species (Stephens et al., 2009) that relies on energy reserves stored during the feeding season to support migratory, maintenance, and reproductive costs throughout the winter months. Ultimately, smaller structural size is expected to limit the amount of reserve mass an individual is able to carry, which may impact their ability to survive and reproduce successfully (Adamczak et al., 2023; Pirotta, 2022). For example, decreasing body size was associated with declining calving probability in North Atlantic right whales (Pirotta et al., 2024; Stewart et al., 2022).…”

“…In critically endangered North Atlantic right whales ( Eubalaena glacialis ), exposure to multiple stressors is hypothesized as the cause of a multidecadal decrease in length (Stewart et al., 2021). In general, understanding how growth patterns vary as a function of habitat quality was identified as a key knowledge gap in a recent review of marine mammal growth (Adamczak et al., 2023), requiring extensive datasets on individual size and morphology.…”