Habitat preferences by individual humpback whale mothers in the Hawaiian breeding grounds vary with the age and size of their calves

We investigated whether calf age and calf size influence habitat choice by humpback whale motherecalf pairs in their breeding grounds. During 1997e2008, we conducted focal follows of motherecalf pairs in Hawaiian waters. Tail-fluke identification photographs and calf lengths (measured through video-grammetry) were obtained. Water depth and sea-bed terrain type were derived from GPS data. Identification photographs were matched so that the habitat choices could be established within breeding seasons. Across 72 motherecalf pairs resighted over various intervals within a breeding season, magnitude of depth change between initial and final sightings increased significantly with resighting interval. There was a significant increase from initial depth to final depth for relatively long resighting intervals (27e51 days), but no significant difference for relatively short resighting intervals (2e26 days). Although there was no preference for sea-bed terrain type by motherecalf pairs at their initial sighting, there was a preference for rugged terrain at their final resighting. A resource selection model indicated that the relative probability of a location being used by a motherecalf pair increased (as a function of water depth and rugged sea-bed terrain type) from initial to final sighting; a finding supported by subsequent tests of habitat preference versus availability. For 96 measured calves, calf length and water depth were positively correlated, even when ordinal day of measurement was controlled for statistically; a finding confirmed by a general linear model that simultaneously investigated the relationship between water depth, sea-bed terrain type, number of escorts, ordinal day and calf size. Thus, both calf age and size influence habitat choice by motherecalf pairs in their breeding grounds. The movement of mothers and their maturing calves into deeper waters where they favour rugged sea-bed terrain appears to be part of a suite of behavioural changes during the pre-migratory phase of residency in the breeding grounds

Research Priorities to Support Effective Manta and Devil Ray Conservation

Manta and devil rays are filter-feeding elasmobranchs that are found circumglobally in tropical and subtropical waters. Although relatively understudied for most of the Twentieth century, public awareness and scientific research on these species has increased dramatically in recent years. Much of this attention has been in response to targeted fisheries, international trade in mobulid products, and a growing concern over the fate of exploited populations. Despite progress in mobulid research, major knowledge gaps still exist, hindering the development of effective management and conservation strategies. We assembled 30 leaders and emerging experts in the fields of mobulid biology, ecology, and conservation to identify pressing knowledge gaps that must be filled to facilitate improved science-based management of these vulnerable species. We highlight focal research topics in the subject areas of taxonomy and diversity, life history, reproduction and nursery areas, population trends, bycatch and fisheries, spatial dynamics and movements, foraging and diving, pollution and contaminants, and sub-lethal impacts. Mobulid rays remain a poorly studied group, and therefore our list of important knowledge gaps is extensive. However, we hope that this identification of high priority knowledge gaps will stimulate and focus future mobulid research

Ecology and social behavior of a resident manta ray (Manta alfredi) population off Maui, Hawaiʻi

Ph.D. University of Hawaii at Manoa 2010.Includes bibliographical references.Findings from this study broaden our understanding of the ecology and behavior of Manta alfredi. Paired-laser photogrammetry, photo-identification, and active tracking were used to investigate a M. alfredi population off Maui, Hawaiʻi. A total of 286 surveys were conducted between 2005 and 2010, resulting in 309 different individual manta rays, of which 163 were sized. A discovery curve showed no asymptotic trend, indicating the number of individuals using the area was much larger than the total identified. Resights and manta follows revealed a minimum home range spanning the four-islands within Maui County with high site fidelity to the study area within and across years by most individuals. There was no evidence of movements to the Big Island, suggesting there are two independent, island-associated stocks. Males, accounting for 51% of the population, were estimated to reach sexual maturity at 2.8 m disc width ( DW) and females at 3.37 m DW. Maximum sizes were much smaller than those reported in other parts of the world indicating geographic variation in size for this species. The mean pregnancy rate was estimated at 0.56 pregnancies/female/year with larger females pregnant more often and more likely in consecutive years. Significantly more mating trains and pregnant females occurred during the winter season. No direct physical competition was observed between males but evidence of mating trains lasting more than one day suggests endurance rivalry, during which larger males may benefit due to greater energy reserves. The absence of individuals less than 2.5 m DW suggests age class segregation is occurring in this population. Shark scars were evident in 24% of individuals and 10% had an amputated or non-functional cephalic fin, likely caused by entanglement in monofilament fishing line. The Maui aggregation site appears to be an important staging area for breeding and parasite removal by members of this population. Late maturity, low fecundity, and the residential nature of individuals in this population make them particularly vulnerable to localized, anthropogenic threats. Implementing successful management practices to reduce the threat of entanglement and of unregulated "swim-with manta ray" programs is recommended

Humpback Whale (Megaptera novaeangliae) Communication: The Context and Potential Functions of Pec-Slapping Behavior on the Hawaiian Wintering Grounds

xvii, 148 leavesHumpback whales display a variety of percussive behaviors that may function as communication between conspecifics. Pectoral-fin slapping behavior is commonly observed in a variety of marine mammals including seals, dolphins, and humpback whales. Data from 5-years of behavioral observations of humpback whales on the Hawaiian wintering grounds were compiled and analyzed. Overall findings suggest pec-slapping behavior is dependent on the performer's age class, sex, and social role. Adult females appear to pec-slap in competition groups in efforts to encourage competition from surrounding males, indicating her readiness to mate. Adult males pec-slap while disaffiliating from other males, possibly in attempts to maintain a non-agonistic male association. Subadult pee slapping is likely a form of "play", an important characteristic in the development, coordination, and learning in young mammals. These discoveries can serve as tools to enhance the interpretation of humpback whale social behavior, and provide a model for understanding other percussive behaviors

Genomic evidence indicates small island-resident populations and sex-biased behaviors of Hawaiian reef Manta Rays

Abstract Background Reef manta rays (Mobula alfredi) are globally distributed in tropical and subtropical seas. Their life history traits (slow growth, late maturity, low reproductive output) make them vulnerable to perturbations and therefore require informed management strategies. Previous studies have reported wide-spread genetic connectivity along continental shelves suggesting high gene flow along continuous habitats spanning hundreds of kilometers. However, in the Hawaiian Islands, tagging and photo-identification evidence suggest island populations are isolated despite proximity, a hypothesis that has not yet been evaluated with genetic data. Results This island-resident hypothesis was tested by analyzing whole mitogenome haplotypes and 2048 nuclear single nucleotide polymorphisms (SNPs) between M. alfredi (n = 38) on Hawaiʻi Island and Maui Nui (the 4-island complex of Maui, Molokaʻi, Lānaʻi and Kahoʻolawe). Strong divergence in the mitogenome (Φ ST  = 0.488) relative to nuclear genome-wide SNPs (neutral F ST = 0.003; outlier F ST = 0.186), and clustering of mitochondrial haplotypes among islands provides robust evidence that female reef manta rays are strongly philopatric and do not migrate between these two island groups. Combined with restricted male-mediated migration, equivalent to a single male moving between islands every 2.2 generations (~ 64 years), we provide evidence these populations are significantly demographically isolated. Estimates of contemporary effective population size (N e ) are 104 (95% CI: 99–110) in Hawaiʻi Island and 129 (95% CI: 122–136) in Maui Nui. Conclusions Concordant with evidence from photo identification and tagging studies, these genetic results indicate reef manta rays in Hawaiʻi have small, genetically-isolated resident island populations. We hypothesize that due to the Island Mass Effect, large islands provide sufficient resources to support resident populations, thereby making crossing deep channels separating island groups unnecessary. Small effective population size, low genetic diversity, and k-selected life history traits make these isolated populations vulnerable to region-specific anthropogenic threats, which include entanglement, boat strikes, and habitat degradation. The long-term persistence of reef manta rays in the Hawaiian Islands will require island-specific management strategies

The complete mitochondrial genome of the Reef Manta Ray, Mobula alfredi, from Hawaii

We provide the complete mitochondrial genome of the reef manta ray, Mobula alfredi, using an ezRAD approach. The total length of the mitogenome was 18,166 bp and contained 13 protein-coding genes, 22 transfer RNAs genes, two ribosomal RNA genes, and one non-coding control region. The gene organization and length are similar to other Mobula species. This reference mitogenome that includes the control region is expected to be a valuable resource for molecular-based species identification, population genomics, and phylogeography

Aerial survey perspectives on humpback whale resiliency in Maui Nui, Hawaiʻi, in the face of an unprecedented North Pacific marine warming event

After decades of population growth, the central stock of the North Pacific population of humpback whales, known as the Hawaiʻi Distinct Population Segment (HDPS), was delisted from its endangered status in 2016. At that time, however, an unprecedented heating event, the Pacific Marine Heatwave (PMH) was already underway. The PMH coincided with reports of major declines of sightings of humpback whales, including calves of the year, on both the Hawaiian wintering grounds and the feeding grounds of Southeast Alaska. To examine the resiliency of the HDPS, we conducted aerial surveys of the high-density Maui Nui region immediately following the PMH event in 2019 and 2020, using distance sampling methods identical to those used in an earlier series (1993–2003). Results showed whale densities at or above those seen earlier, with mean density for 2020 highest overall. Crude birth rates (percent groups containing a calf) were similarly comparable to those recorded in the earlier series, with an increase from 2019 to 2020. Overall, results suggest the central North Pacific humpback whale population stock to be resilient in the face of this major climatic event

Penis extrusions by humpback whales (Megaptera novaeangliae) on the Hawaiian winter grounds.

The annual winter assembly of humpback whales (Megaptera novaeangliae) in tropical waters has been linked to reproductive activities, including birthing, calf-rearing, and mating. However, the sexual behaviour of this species remains largely undescribed and mating has never been witnessed. We examined 121 h of underwater videotaped footage of humpback whales obtained over five winter seasons in Hawaiian waters for evidence of penis extrusions by whales engaged in various activities in a range of social groups. In 630 different pods containing videotaped males, we noted 13 penis extrusion incidents. Penis extrusions were performed by lone singers (2 incidents), by the single escort to a mother/calf pair (6 incidents), and by principal and secondary escorts in competitive pods containing a female either with a calf (2 incidents) or without (3 incidents). All penis extrusions were brief (mean=44.0) s). Body length measurements (mean=11.53 m, SD=0.46 m, range=10.64 m to 12.05 m) were obtained using underwater videogrammetry on seven penis extruders, and suggested that the majority were sexually mature. Each penis extrusion in a competitive pod coincided with the penis extruder chasing another whale, and in four of five cases appeared to be directed toward another male. In the remaining case, the extruder appeared to attempt mating with a mother. Our findings suggest that penis extrusions in humpback whale competitive pods are often a concomitant of dominance contests between males