Carcasses on the coastline: measuring the ecological fidelity of the cetacean stranding record in the eastern North Pacific Ocean

Abstract

Abstract.-To understand how well fossil assemblages represent original communities, paleoecologists seek comparisons between death assemblages and their source communities. These comparisons have traditionally used nearshore, marine invertebrate assemblages for their logistical ease, high abundance, and comparable census data from living communities. For large marine vertebrates, like cetaceans, measuring their diversity in ocean ecosystems is difficult and expensive. Cetaceans, however, often beach or strand themselves along the coast, and archived data on stranded cetaceans have been recorded, in some areas, over several decades. If the stranding record is interpreted as a death assemblage, then the stranding record may represent a viable alternative for measuring diversity in living communities on directly adjacent coastlines. This study assessed the fidelity of the cetacean stranding record in the eastern North Pacific Ocean. The living community in this region has been studied for over 100 years and, recently, extensive and systematic live transect surveys using ship-based observing platforms have produced a valuable source of live diversity data. Over this same period, the U.S. Marine Mammal Stranding Program has collected and archived a record of cetacean strandings along the U.S. Pacific coastline, providing an ideal death assemblage for comparison. Using fidelity metrics commonly used in marine invertebrate taphonomy, I determined that the stranding record samples the living cetacean community with high fidelity, across fine and coarse taxonomic ranks, and at large geographic scales (.1000 km of coastline). The stranding record is also richer than the live surveys, with live-dead ratios between 1.1 and 1.3. The stranding record recovers similar rank-order relative abundances as live surveys, with statistical significance. Also, I applied sample-based rarefaction methods to generate collector's curves for strandings along the U.S. Pacific Coast to better evaluate the spatiotemporal characteristics of the stranding record. Results indicate that saturation (i.e., sampling .95% assemblage) at species, genus, and family levels occurs in less than five years of sampling, with families accumulating faster than species, and larger geographic regions (i.e., longer coastlines) accumulating taxa the most rapidly. The high fidelity of the stranding record, measured both in richness and by ranked relative abundance, implies that ecological structure from living cetacean communities is recorded in the death assemblage, a finding that parallels marine invertebrate assemblages, though at far larger spatial scales. These results have implications for studying cetacean ecology in both modern and ancient environments: first, these results imply that the stranding record, over sufficiently long time intervals, yields a richer assemblage than using linetransect methods, and faithfully records aspects of community structure; and second, these results imply that geochronologically well-constrained fossil cetacean assemblages ...

The high fidelity of the cetacean stranding record: insights into measuring diversity by integrating taphonomy and macroecology

“…'dolphin species'). Therefore, I pooled each dataset into a taxonomic hierarchy of exclusively species-, genus-and family-level data, following methods outlined by Pyenson [22].…”

“…Previously, researchers have asked similar questions about the fidelity of the cetacean stranding record for discrete taxonomic groups [23], specific geographical regions or across specific spans of time [18,19,24], but none of these aforementioned studies used metrics to quantify fidelity in a comparable manner. Recently, Pyenson [22] explicitly implemented such fidelity metrics to demonstrate that the cetacean stranding record along the Pacific coastline of the continental US faithfully captured ecological information about the adjacent living community in the eastern North Pacific ocean.…”

“…A total of 1 283 988 individual sighting records and 12 847 individual stranding occurrences (including New Zealand) were compiled for this study (electronic supplementary material, table S1). Fidelity metrics, which have predominantly been successful at resolving live-dead comparisons in marine invertebrate assemblages [25 -27], provided a quantitative framework for comparing live -dead datasets for cetaceans [22]. Also, sample-based rarefaction analyses illuminated the sampling characteristics of strandings on different coastlines.…”

Late Pleistocene gray whales (Eschrichtius robustus) offshore Georgia, U.S.A., and the antiquity of gray whale migration in the North Atlantic Ocean

“…Based on mortality and strandings rates, argued that the seafloor will be the end destination of the majority of gray whale mortalities, although the persistence of such carcasses may differ based on scavenging, depositional environment, and whalefall community turnover. The notion that the seafloor adjacent to long coastlines samples cetacean diversity is reinforced by recent studies of the stranding record by Pyenson (2010Pyenson ( , 2011, who demonstrated that the richness and abundances of cetacean strandings at decadal-scale temporal and continental-scale geographic sampling regimes can provide faithful measures of diversity in living communities.…”

“…The decay and decomposition of marine mammals have been topics of study since Weigelt (1989)'s seminar work in the early twentieth century, although there have only been a handful of case studies that have investigated the actualistic taphonomy of marine mammals in a quantitative or operational manner (Schäfer, 1972;Liebig et al, 2003Liebig et al, , 2007; also see discussion in Pyenson, 2010). In a landmark work, Schäfer (1972) outlined a general pathway for the drift, decay and final burial of cetacean carcasses in a nearshore environment, based on observations of small odontocetes in the North Sea.…”