Ontogenetic niche structure and partitioning of immature sandbar sharks within the Chesapeake Bay nursery

• Published in: Marine biology 2022-06, Vol.169 (6), Article 76
• Main Authors: Latour, Robert J., Gartland, James, Peterson, Cassidy D.
• Format: Article
• Language: English
• Subjects: Abiotic factors; Abundance; Analysis; Biomedical and Life Sciences; Carcharhinus plumbeus; Coexistence; Competitors; Dissolved oxygen; Ecological distribution; Ecological effects; Ecological niches; Ecosystem biology; Ecosystem components; Ecosystem structure; Ecosystems; Equivalence; Fisheries; Freshwater & Marine Ecology; Genetic aspects; Habitat utilization; Habitats; Identification and classification; Juveniles; Life Sciences; Longline fishing; Marine & Freshwater Sciences; Marine biology; Marine fishes; Microbiology; Neonates; Niche (Ecology); Niche overlap; Niches; Nurseries; Nursery grounds; Oceanography; Ontogeny; Original Paper; Partitioning; Relative abundance; Sand bars; Separation; Sharks; Statistical analysis; Surveying; Zoology
• ISSN: 0025-3162; 1432-1793
• DOI: 10.1007/s00227-022-04066-3

Characterizing ontogenetic niches of species is fundamental to understanding ecosystem structure and how habitat utilization changes across life-stages. Niche partitioning over temporal and spatial domains is also key to the coexistence of interspecific and intraspecific competitors. This study utilized fisheries-independent bottom longline survey data collected from 2013 to 2020 to develop ecological niche models for neonate and juvenile sandbar sharks ( Carcharhinus plumbeus ) inhabiting the lower Chesapeake Bay nursery area. Modeled relationships in combination with auxiliary environmental data yielded size-specific habitat suitability estimates that were used to develop projected spatiotemporal distributions and assess ontogenetic niche equivalency. Results showed appreciable differences among the two size-classes in the relationships of relative abundance with measured abiotic variables. High neonate (observed size range 45.5–70.5 cm total length, TL) relative abundance was associated with high bottom temperatures, low bottom dissolved oxygen levels, and intermediate depths and bottom salinities. In contrast, high juvenile (observed size range 71–116 cm TL) relative abundance was linked with intermediate bottom temperatures and bottom dissolved oxygen levels, deeper depths, and lower bottom salinities. Fine-scale coexistence among the two size-classes was low, and annual maps of projected habitat suitabilities showed temporally consistent spatial separation of favorable abiotic niche conditions for neonates and juveniles. Niche equivalency results revealed that overlap among the size-specific niches was low to moderate with statistically significant differences detected annually and seasonally within years. Taken together, these results yield valuable insights on neonate and juvenile sandbar shark ecology by providing a nuanced delineation of stage-specific ecological niches and evidence of niche separation within a large nursery ecosystem.