Patterns of Use of Maku'a Beach, O'ahu, Hawai'i, by Spinner Dolphins (<I>Stenella longirostris</I>) and Potential Effects of Swimmers on Their Behavior

Abstract

Spinner dolphins (Stenella longirostris) use Maku'a Beach, a small bight along the Wa'i'ana'e coast of O'ahu, as a rest site. Behavior and use patterns of Maku'a Beach by spinner dolphins and swimmers were studied in July and August of 1995 to provide baseline data on the dolphin population and to assess potential impacts of swimmers on the dolphins' resting behavior. Dolphins were observed on 52 out of 53 days, and they entered the area between 0545 and 0845 h. Their departure time varied widely. Average school size was 67 ± 0.6 SE and decreased with time of day. The most common aerial behaviors were slaps, leaps, and spins, respectively, with a peak in aerial behavior in late afternoon associated with schools moving offshore. The number of swimmers in the study area was highest on weekend mornings (xstudy area was highest on weekend mornings (study area was highest on weekend mornings (= 12 ± 0.6 SE), with a maximum of 63 people in the water at the same time. Rest appeared delayed and compressed in this population of dolphins as compared to other studies and may be a response to the presence of swimmers in the morning. The results suggest a potential adverse impact of swimmers on the dolphins' resting patterns, with earlier departure times and shorter periods of dive behavior indicative of rest.

Passive acoustic monitoring of coastally associated Hawaiian spinner dolphins, Stenella longirostris, ground-truthed through visual surveys

“…Neither of these previous studies made observations in Bay 1, the bay with the highest values for presence here. Overall, the values from studies on the Kona Coast are lower when compared to a study done on Oahu where researchers observed spinner dolphins on 98% of days at Makua Beach (52 of 53) (Danil et al, 2005).…”

Close approaches by vessels elicit surface active behaviors by southern resident killer whales

“…Several studies have also shown that cetaceans perform SABs in response to disturbance. The performance of SABs are common reactions to biopsy sampling (Weinrich et al 1992, Clapham & Mattila 1993, Brown et al 1994, Gauthier & Sears 1999, Hooker et al 2001) and approaches by vessels and swimmers (Weinrich et al 2001, Williams et al 2002a,b, Coscarella et al 2003, Danil et al 2005, Lusseau 2006a. Similarly, the findings in the present study that more SABs were performed when vessels approached whales closely and that the majority of SAB bouts were performed near the time of the POCA suggest that close approaches and/or changes in vessel behavior or distance may elicit SAB performance in southern resident killer whales.…”

“…These include: decreased use of primary habitats (Allen & Read 2000, Lusseau 2005), altered spatial distribution among individuals (Au & Perryman 1982, Bejder et al 1999, 2006, Nowacek et al 2001, Jelinski et al 2002, altered behavioral budgets (Chilvers et al 2003, Coscarella et al 2003, Lusseau 2003a, Constantine et al 2004, King & Heinen 2004, Lemon et al 2006, Williams et al 2006, Hodgson & Marsh 2007), changed swimming speed or direction (Au & Perryman 1982, Kruse 1991, Au & Green 2000, Nowacek et al 2001, Williams et al 2002a,b, Jahoda et al 2003, Lusseau 2003b, Ng & Leung 2003, Bejder et al 2006, Lemon et al 2006, Williams & Ashe 2007 and altered surface and dive durations (Janik & Thompson 1996, Au & Green 2000, Jahoda et al 2003, Lusseau 2003a, b, Ng & Leung 2003. Surface active behaviors (SABs), such as tail slaps, pectoral fin slaps, leaps and jumps, may also be displayed in response to approaching vessels (Weinrich et al 2001, Williams et al 2002a, Coscarella et al 2003, Danil et al 2005, Lusseau 2006a.…”

The use of area–time closures as a tool to manage cetacean-watch tourism

“…This predictable behaviour and their daytime reliance on sheltered bays that are easily accessible by people (see Figure 17.1) render them more exposed and more susceptible to human disturbance compared with other dolphin species. Recent studies suggest that the resting periods for Hawaiian spinner dolphins may be interrupted or truncated by exposure to human activity, but the biological significance of these impacts requires further investigation (Danil et al, 2005;Delfour, 2007;Courbis & Timmel, 2009). Furthermore, the population of spinner dolphins along the Kona Coast of Hawai'i Island, which is the target for large-scale cetacean-watch operations, is genetically distinct from all other spinner dolphin populations in the Hawaiian Archipelago (Andrews et al, 2010).…”