Abstract
Marine protected areas (MPAs) are increasingly being used as a conservation tool for highly mobile marine vertebrates and the focus is typically on protecting breeding areas where individuals are aggregated seasonally. Yet movements during the non-breeding season can overlap with threats that may be equally as important to population dynamics. Thus understanding habitat use and movements of species during the non-breeding periods is critical for conservation. Glacier Bay National Park, Alaska, is one of the largest marine mammal protected areas in the world and has the only enforceable protection measures for reducing disturbance to harbor seals in the United States. Yet harbor seals have declined by up to 11.5%/year from 1992 to 2009. We used satellite-linked transmitters that were attached to 37 female harbor seals to quantify the post-breeding season migrations of seals and the amount of time that seals spent inside vs. outside of the MPA of Glacier Bay. Harbor seals traveled extensively beyond the boundaries of the MPA of Glacier Bay during the post-breeding season, encompassing an area (25,325 km2) significantly larger than that used by seals during the breeding season (8,125 km2). These movements included the longest migration yet recorded for a harbor seal (3,411 km) and extended use (up to 23 days) of pelagic areas by some seals. Although the collective utilization distribution of harbor seals during the post-breeding season was quite expansive, there was a substantial degree of individual variability in the percentage of days that seals spent in the MPA. Nevertheless, harbor seals demonstrated a high degree of inter-annual site fidelity (93%) to Glacier Bay the following breeding season. Our results highlight the importance of understanding the threats that seals may interact with outside of the boundaries of the MPA of Glacier Bay for understanding population dynamics of seals in Glacier Bay.
Highlights
Two common objectives for marine protected areas (MPAs) are enhancement of commercial fisheries for sustaining or rebuilding yield, and conservation of biodiversity [1,2,3]
Ethics Statement All harbor seal capture, handling, and research was conducted under Marine Mammal Protection Act (MMPA) permit numbers 358-1787-00 and 358-1787-01 issued to the Alaska Department of Fish & Game and MMPA permit number 782-1676-02 issued to the National Marine Mammal Laboratory by National Oceanic and Atmospheric Administration (NOAA) -Protected Resources Division
Whereas the glacial ice breeding area of Johns Hopkins Inlet encompasses approximately 22 km2, the area used by seals during the post-breeding season encompassed approximately 25,000 km2 of which only 2,400 km2 was in the MPA of Glacier Bay
Summary
Two common objectives for marine protected areas (MPAs) are enhancement of commercial fisheries for sustaining or rebuilding yield, and conservation of biodiversity [1,2,3]. MPA designation can be less than effective in meeting conservation goals for highly mobile marine taxa for a number of reasons. The timing and location of the MPAs should correspond to the temporal and spatial distribution of the threat, the actual designation of the MPA boundaries more likely reflects trade-offs between sociocultural, economic, and biological factors [11,12]. The vaquita (Phocoena sinus) provides a good example where a clearly defined population threat such as bycatch [13] can be mitigated with a simple MPA-based solution by expanding existing MPA boundaries [14] but economic constraints prevents its implementation sufficiently to meet the conservation objectives. MPAs may not meet species conservation objectives because they may not correspond temporally or spatially with the most pressing threat to the population [15]. Research demonstrates that major threats may occur during post breeding migrations [16] or during dispersal of juveniles [17]
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