Tim Gerrodette

• Southwest Fisheries Science Center

Information regarding beaked whales is so sparse that even the most basic aspects of their biology, such as their distribution, remain poorly defined for some species. We have reviewed the known distribution of each beaked whale species and where possible, used this information to infer its global distribution. While for some species, such as the r...

A twelve-year hiatus in fishery-independent marine mammal surveys in the eastern tropical Pacific Ocean (ETP), combined with a mandate to monitor dolphin stock status under international agreements and the need for reliable stock status information to set dolphin bycatch limits in the tuna purse-seine fishery, has renewed debate about how best to a...

In 2018, it was estimated that fewer than 20 of Mexico’s endemic vaquita porpoise Phocoena sinus remained, and the species was declining by 47% yr ⁻¹ . Entanglement in gillnets is the sole threat to the species, and since the last population size estimate, gillnetting has increased in the small area where most vaquitas remain—a 12 × 24 km area in t...

Multispecies aggregations of tuna, dolphins, and seabirds are prevalent and conspicuous in the vast waters of the eastern tropical Pacific and form the basis of a commercial fishery for yellowfin tuna (Thunnus albacares) through setting on schools of dolphins, which is among the largest tuna fisheries in the world. Incidental dolphin mortality asso...

Runs of homozygosity (ROH) occur when offspring inherit haplotypes that are identical by descent from each parent. Length distributions of ROH are informative about population history; specifically, the probability of inbreeding mediated by mating system and/or population demography. Here, we investigate whether variation in killer whale (Orcinus o...

Runs of homozygosity (ROH) occur when offspring inherit haplotypes that are identical by descent from each parent. Length distributions of ROH are informative about population history; specifically the probability of inbreeding mediated by mating system and/or population demography. Here, we investigate whether variation in killer whale (Orcinus or...

Understanding the effect of stage‐specific traits on species feeding habits can reveal how natural selection shapes life strategies. Amino acid (AA) nitrogen stable isotopes (δ¹⁵N) provide multiple proxies of habitat baseline values and diet that can improve our understanding of species feeding strategies relative to their animal metabolism. We eva...

Baseline knowledge of spatial and temporal distribution patterns is essential for cetacean management and conservation. Such knowledge is particularly important in areas where gillnet fishing occurs, as the Upper Gulf of California, which increases the probability of bycatch of cetaceans. In this area, the vaquita porpoise ( Phocoena sinus ) has be...

Reconstruction of the demographic and evolutionary history of populations assuming a consensus tree‐like relationship can mask more complex scenarios, which are prevalent in nature. An emerging genomic toolset, which has been most comprehensively harnessed in the reconstruction of human evolutionary history, enables molecular ecologists to elucidat...

Estimating the number of dolphins in a group is a challenging task. To assess the accuracy and precision of dolphin group size estimates, observer estimates were compared to counts from large‐format vertical aerial photographs. During 11 research cruises, a total of 2,435 size estimates of 434 groups were made by 59 observers. Observer estimates we...

Distance sampling is a widely used method for estimating wildlife population abundance. The fact that conventional distance sampling methods are partly design-based constrains the spatial resolution at which animal density can be estimated using these methods. Estimates are usually obtained at survey stratum level. For an endangered species such as...

Aim To develop a more ecologically realistic approach for estimating the population size of cetaceans and other highly mobile species with dynamic spatial distributions. Location California Current Ecosystem, USA . Methods Conventional spatial density models assume a constant relationship between densities and habitat covariates over some time pe...

Climate variability alters nitrogen cycling, primary productivity, and dissolved oxygen concentration in marine ecosystems. We examined the role of this variability (as measured by six variables) on food chain length (FCL) in the California Current (CC) by reconstructing a time series of amino acid–specific δ¹⁵N values derived from common dolphins,...

Monitoring and assessment of the status of marine mammal populations is a requirement of the European Marine Strategy Framework Directive (MSFD). Due to the difficulty of collecting data in the marine environment and because many populations of these highly mobile species inhabit waters of several Member States, monitoring of marine mammals is part...

The number of Mexico's endemic porpoise, the vaquita (Phocoena sinus), is collapsing primarily due to bycatch in illegal gillnets set for totoaba (Totoaba macdonaldi), an endangered fish whose swim bladders are exported to China. Previous research estimated that vaquitas declined from about 567 to 245 individuals between 1997 and 2008. Acoustic mon...

The vaquita (Phocoena sinus) is the world's most endangered marine mammal with ≈245 individuals remaining in 2008. This species of porpoise is endemic to the northern Gulf of California, Mexico, and has historically suffered population declines from unsustainable bycatch in gillnets. An illegal gillnet fishery for an endangered fish, the totoaba (T...

Reproductive parameters were estimated and compared for eastern North Pacific populations of common dolphins using specimen and photogrammetric data. Age and length data for Delphinus capensis and D. delphis specimens recovered as bycatch or strandings were used to estimate the postnatal growth rates needed to estimate age for calves measured in ae...

Distance sampling is a widely used method for estimating wildlife population abundance. Conventional design-based distance sampling approaches allow us to estimate animal abundance in the study region without modelling the spatial distribution of animals, and in doing this the spatial information is often ignored. More sophisticated model-based app...

[This corrects the article DOI: 10.1098/rsos.150628.].

The Spanish multidisciplinary survey PELACUS is carried out annually to study pelagic marine ecosystem and evaluate fishing resources of the North and Northwest shelf waters of the Iberian Peninsula. Linear transects perpendicular to the coast distant 8 nm each and up to the 1000 m isobath are prospected acoustically at a speed of 10 knots between...

Bayesian statistics, in contrast to classical statistics, uses probability to represent uncertainty about the state of knowledge. Bayesian statistics has often been associated with the idea that knowledge is subjective and that a probability distribution represents a personal degree of belief. Dr. Daniel Goodman considered this viewpoint problemati...

Bayesian statistics, in contrast to classical statistics, uses probability to represent uncertainty about the state of knowledge. Bayesian statistics has often been associated with the idea that knowledge is subjective and that a probability distribution represents a personal degree of belief. Dr. Daniel Goodman considered this viewpoint problemati...

The pressures on coastal marine mammals are increasing as the world’s human population rises and with it the consequential expansion in world trade and port developments, and the continued movement of people to the coastal zone. Monitoring the effect of coastal development on marine mammals is challenging because: (1) the impacts of coastal develop...

In the eastern tropical Pacific Ocean, yellowfin tuna (Thunnus albacares) are often found in association with spotted (Stenella attenuata) and spinner (Stenella longirostris) dolphins. Purse-seine vessels use this co-occurrence to locate the tuna by searching for dolphins and associated birds. Data collected by onboard observers since the late 1970...

California sea lions increased from approximately 50 000 to 340 000 animals in the last 40 years, and their pups are starving and stranding on beaches in southern California, raising questions about the adequacy of their food supply. We investigated whether the declining sea lion pup weight at San Miguel rookery was associated with changes in abund...

El objetivo de las Estrategias Marinas es permitir el uso sostenible del medio marino mediante la gestión de las actividades y presiones humanas siguiendo un enfoque ecosistémico. La evaluación del estado de conservación de las especies marinas y su monitorización para determinar si alcanza el Buen Estado Ambiental (BEA) son sus pilares básicos. Pa...

Common dolphins (Delphinus delphis) are one of the most abundant species of small cetacean in Northeast Atlantic Ocean and the most abundant in Atlantic shelf waters of the Iberian Peninsula. However, the abundance, distribution and population trends in the recent years of this species are poorly known, but such information is needed to develop pop...

We inferred the population densities of blue whales (Balaenoptera musculus) and short-beaked common dolphins (Delphinus delphis) in the Northeast Pacific Ocean as functions of the water-column’s physical structure by implementing hierarchical models in a Bayesian framework. This approach allowed us to propagate the uncertainty of the field observat...

Background/Question/Methods In marine ecosystems, climate change is altering biochemical cycling, the distribution of species and food web structure, but it is unknown the magnitude of such changes. In recent decades, the highly productive California Current System has experienced increasing frequencies of El Niño-Southern Oscillation (ENSO) even...

Gray seals were first observed breeding in the Dutch Wadden Sea in 1985, after centuries of absence. The breeding colony there is now the largest on the European continent. We describe the changes in gray seal numbers and their geographical expansion, and estimate how these processes were influenced by immigration from other colonies. Counts of hau...

A small porpoise (Phocoena sinus) found only in the upper Gulf of California is called vaquita and is the most endangered species of marine mammal in the world. A rough projection using the last abundance estimate in 1997 and mortality in gillnets resulted in an estimate of only about 150 vaquitas remaining prior to the 2008 survey. With so few vaq...

Because consumers integrate components of their habitat through diet over time and space, stable isotope ratios from animal tissues can track spatial variation in baseline values across marine systems. To understand large-scale geographic patterns in the eastern Pacific ocean, muscle δ13C and δ15N from epi-mesopelagic squid (n = 404) were collected...

An ecosystem approach to fisheries management is a widely recognized goal, but describing and measuring the effects of a fishery on an ecosystem is difficult. Ecological information on the entire catch (all animals removed, whether retained or discarded) of both species targeted by the fishery and nontarget species (i.e., bycatch) is required. We u...

Cetacean sighting data collected under various programmes in Colombian Pacific waters were collated with the goal of assessing the distribution and abundance patterns of all species occurring in the exclusive economic zone (EEZ). Distribution maps are presented for 19 species and one genus based on 603 sightings collected between 1986 and 2008. Ord...

A basic principle of effective resource management is that decisions should be conservative in the face of uncertainty. Due to limited data, there is often considerable uncertainty about species' habitat relationships and requirements. If the boundaries of a protected area are based on relationships estimated by a habitat model, effective managemen...

The vaquita (Phocoena sinus) is a critically endangered small cetacean found only in the upper Gulf of California, where fisheries bycatch remains an acute threat. Cost, shallow heavily fished areas, and the vaquitas extreme avoidance of noisy motorized vessels argue against using large vessels typically used for visual line transect surveys. Towed...

Despite more than half a century of criticism, significance testing continues to be used commonly by ecologists. Significance tests are widely misused and misunderstood, and even when properly used, they are not very informative for most ecological data. Problems of misuse and misinterpretation include: (i) invalid logic; (ii) rote use; (iii) equat...

The Mexican Pacific Ocean, defined as east of 122°W and from 12 to 34° N, encompasses an oceanographic transition zone with dynamic population and community processes. In order to gain insight into possible marine mammal ecological responses to the current rapid environmental changes, we compiled and analyzed data from 11 145 marine mammal sighting...

Predicted current patterns of global marine mammal species richness based on different presence thresholds. Relative environmental suitability (RES) threshold for assumed species presence in 0.5° grid cells (1990s). A. RES>0, B. RES>0.2, C. RES>0.4, D. RES>0.6, E. RES>0.8. Biodiversity hotspots in maps based on higher assumed RES thresholds represe...

Summary of validation results comparing observed versus predicted species occurrence per 5° grid cell in different survey areas. Red values represent models with lowest AIC, yellow values correspond to models falling into the range of ΔAIC <2 and grey cells represent models with non-significant relationships. (PDF)

Quantifying the spatial distribution of taxa is an important prerequisite for the preservation of biodiversity, and can provide a baseline against which to measure the impacts of climate change. Here we analyse patterns of marine mammal species richness based on predictions of global distributional ranges for 115 species, including all extant pinni...

AbstractA line-transect survey for the critically endangered vaquita, Phocoena sinus, was carried out in October–November 2008, in the northern Gulf of California, Mexico. Areas with deeper water were sampled visually from a large research vessel, while shallow water areas were covered by a sailboat towing an acoustic array. Total vaquita abundance...

Bycatch in artisanal gill nets threatens the vaquita, Phocoena sinus, with extinction. In 2008 the Mexican government announced a conservation action plan for this porpoise, with three options for a protected area closed to gill net fishing. The probability of success of each of the three options was estimated with a Bayesian population model, wher...

The Mexican Pacific Ocean, defined as east of 122°W and from 12 to 34° N, encompasses an oceanographic transition zone with dynamic population and community processes. In order to gain insight into possible marine mammal ecological responses to the current rapid environmental changes, we compiled and analyzed data from 11 145 marine mammal sighting...

Line-transect ship surveys are the primary method used to estimate abundance of pelagic cetaceans. However, survey methods are often modified from traditional methods because observers must approach cetacean groups to identify species and estimate group size. Returning to the trackline after approaching a school dramatically reduces the amount of e...

For the past half-century, the purse seine fishery for yellowfin tuna has been a significant factor in the lives of dolphins in the eastern tropical Pacific (ETP). However, little is known about how frequently an individual dolphin is exposed to the fishery, and there are no methods available for accurately assessing the prior exposure of dolphins...

High female mortality due to male aggression in Hawaiian monk seals led us to investigate the role of habitat use and social structure on sex ratios and aggression at Laysan Island, Hawaii. The sex ratio was strongly skewed towards males in the early 1980s and this, combined with the social structure, asynchronous reproduction, and terrestrial habi...

This chapter discusses the ecological association of tuna and dolphins. In the tropical waters of the Pacific Ocean west of Mexico and Central America, large yellow fin tuna (. Thunnus albacares) swim together with several species of dolphins: pantropical spotted (. Stenella attenuata), spinner (. S. longirostris), and common (. Delphinus delphis a...

Background/Question/Methods Biodiversity hotspots have received much attention but relatively little is known about hotspots in oceanic systems (waters seaward of the continental shelf). We describe density and species richness hotspots for cetaceans in the eastern tropical Pacific, a geographic area of approximately 21 million km2 encompassing the...

Line-transect analysis is a widely used method of estimating plant and animal density and abundance. A Bayesian approach to a basic line-transect analysis is developed for a half-normal detection function. We extend the model of Karunamuni and Quinn [Karunamuni, R.J., Quinn II, T.J., 1995. Bayesian estimation of animal abundance for line-transect s...

To meet the information needs of the Navy and other users of the marine environment, cetacean density is modeled as a continuous function of oceanographic variables for 12 species in the California Current Ecosystem (CCE) and 15 species in the Eastern Tropical Pacific (ETP) based on line-transect surveys conducted from 1986 to 2003. Models are vali...

Reproductive data for 2 pelagic dolphin subspecies in the eastern tropical Pacific, the eastern spinner (ES) dolphin Stenella longirostris orientalis and northeastern pantropical spotted (NEPS) dolphin S. attenuata attenuata, were obtained from aerial photographs taken between 1987 and 2003. Two measures of reproductive output were estimated: propo...

García, C.; Avila, I.C.; Palacios, D.; Gerrodette, T.; Suárez, M.; Soler, G.; Rasmussen, K.; May-Collado, L.; Parson, C.; Trujillo, F. & Bessudo, S. 2008. Presence, distribution and threats of Stenella attenuata and Tursiops truncatus in the Pacific waters of Panamá and Colombia. Abstract 310 in Memories of the XIII Reunión de Trabajo de Especialis...

Distribution and prevalence of the phoretic barnacle Xenobalanus on cetacean species are reported for 22 cetaceans in the eastern tropical Pacific Ocean (21 million km2). Four cetacean species are newly reported hosts for Xenobalanus: Bryde's whale (Balaenoptera edeni), long-beaked common dolphin (Delphinus capensis), humpback whale (Megaptera nova...

Research into the effects of scale on cetacean-habitat relationships is limited and has produced ambiguous results. We explored the effects of spatial resolution (a component of scale) on dolphin- habitat models using 4 yr of data collected in the eastern tropical Pacific Ocean (ETP). We developed generalized additive models of dolphin-habitat rela...

We assess the status of 2 dolphin stocks affected by purse-seine fishing in the eastern topical Pacific and evaluate hypotheses for their lack of re- covery. We use Bayesian methods and fit generalized models of logistic population growth to abundance estimates for northeastern offshore spotted dolphins Stenella attenuata attenuata and eastern spin...

Blue whale locations in the Southern Hemisphere and northern Indian Ocean were obtained from catches (303 239), sightings (4383 records of ≥8058 whales), strandings (103), Discovery marks (2191) and recoveries (95), and acoustic recordings. Sighting surveys included 7 480 450 km of effort plus 14 676 days with unmeasured effort. Groups usually cons...

We assessed scientists' ability to detect declines of marine mammal stocks based on recent levels of survey effort, when the actual decline is precipitous. We defined a precipitous decline as a 50% decrease in abundance in 15 yr, at which point a stock could be legally classified as “depleted” under the U.S. Marine Mammal Protection Act. We assesse...

The first at-sea estimates of density and abundance of the olive ridley turtle Lepi- dochelys olivacea in the eastern tropical Pacific (ETP) were produced from shipboard line-transect data. Multi-ship surveys were conducted in 1992, 1998, 1999, 2000, 2003, and 2006 in the area defined by 5° N, 120° W, and 25° N and the coastline of Mexico and Centr...

A bstract The kill of dolphins ( Stenella attenuata and S. longirostris ) in the eastern tropical Pacific tuna purse‐seine fishery has been underestimated because of unobserved deaths of nursing calves due to separation from their mothers during fishing. Based on an analysis of dolphins killed from 1973 to 1990, and depending on the length at which...

We use temporally dynamic environmental variables and fixed geographic variables to construct generalized additive models to predict delphinid (family Delphinidae) encounter rates (number of groups per unit survey effort) and group sizes in the eastern tropical Pacific Ocean. The delphinid sighting data and environmental data were collected simulta...

Temporally dynamic environmental variables and fixed geographic variables were used to construct generalised additive models to predict Cuvier’s (Ziphius cavirostris) and Mesoplodon beaked whale encounter rates (number of groups per unit survey effort) and group sizes in the eastern tropical Pacific Ocean. The beaked whale sightings and environment...

Nineteen species of cetaceans (families Balaenopteridae, Kogiidae, Physeteridae, Ziphiidae and Delphinidae) occur in the Costa Rican Pacific Exclusive Economic Zone (EEZ). Based on data recorded from the EEZ by the Southwest Fisheries Service Center, Cascadia Research Collective, and CIMAR between 1979-2001, we mapped the distribution of 18 cetacea...

Populations of northeastern offshore spotted dolphins Stenella attenuata attenuata and eastern spinner dolphins S. longirostris orientalis have been reduced because the dolphins are bycatch in the purse-seine fishery for yellowfin tuna in the eastern tropical Pacific Ocean (the 'tuna-dolphin issue'). Abundance and trends of these dolphin stocks wer...

Estimating the abundance and density of beaked whales is more difficult than for most other cetacean species. Consequently few estimates appear in the published literature. Field identification is problematic, especially for the smaller species, and visual detecti on rates decrease dramatically with Beaufort sea state; prior experience is very impo...

We estimated the total number of pantropical spotted dolphin (Stenella attenuata) mothers killed without their calves ("calf deficit") in all tuna purse-seine sets from 1973-90 and 1996-2000 in the eastern tropical Pacific. Estimates were based on a tally of the mothers killed as reported by color pattern and gender, several color-pattern-based fre...

Summary form only given. Cetacean abundance in the eastern tropical Pacific is based on large-scale line-transect surveys covering 6% of the world ocean. Cruises using 2 vessels for 4 months each were carried out in 8 years between 1986 and 2000. Thirty cetacean species were recorded, over 1/3 of the world total. Abundance is estimated with a modif...

To identify and quantify spatial patterns in cetacean density in the eastern Pacific Ocean, we have built generalized additive models (GAMs) of encounter rate (number of sightings per km) and average school size based on the Southwest Fisheries Science Center's 1986-96 survey data. The survey area encompassed over 25 million sq. km, and the trackli...

The distances to 1,576 targets between 0.3 and 10.4km from two ships were measured using the reticle scale in 253 binoculars during cetacean surveys in the eastern tropical Pacific Ocean. Distances were measured under a range of conditions representing the environmental variability in three years of field surveys. Alternative formulae for calculati...

A more precautionary approach to marine fishery management is much needed, but a central issue is how decisions are made when, as is usual, uncertainties are large. Reversing the burden of proof(showing that a given fishing level is safe before allowing it) is a necessary but not sufficient condition for a precautionary approach. Several policy asp...

Estimates of cetacean abundance from transect surveys rely on unbiased estimates of group size, but estimating the size of a large school of active animals is a difficult task. To evaluate the bias and precision of estimates of dolphin group sizes, we compared estimates made from ships with counts based on aerial photographs taken from a helicopter...

The most recent round of line-transect surveys to estimate cetacean abundance in the Eastern Tropical Pacific (ETP) was conducted by the Southwest Fisheries Science Center (SWFSC) over a three-year period from 1998-2000. These methods assume that animals do not react to the ship before they are sighted and all animals on the trackline are detected....

Factors that affect cetacean perpendicular sighting distances are investigated using a Generalised Additive Modelling (GAM) framework to analyse 8,203 sightings of 34 cetacean species seen on 200,000km of shipboard line-transect surveys in the eastern Pacific in 1986-96. Perpendicular sighting distance is modelled as a non-linear function of the fo...

A bstract A line‐transect survey specifically designed to estimate vaquita ( Phocoena sinus ) abundance over its entire range was carried out by three boats in the summer of 1997. There was a total of 125 sightings of vaquita groups, mainly due to the use of large 25 ± 150 binoculars, which were seven times more effective in detecting vaquitas than...

Acoustic backscatter data from a 38-kHz echo sounder and a 150-kHz acoustic Doppler current profiler (ADCP) were collected during Southwest Fisheries Science Center marine mammal surveys in the eastern Pacific aboard the NOAA ship David Starr Jordan in 1992 and 1993. These data were processed to give profiles of volume scattering strength. A deep s...

A bstract The abundance of the only population of vaquitas, Gulf of California harbor porpoise ( Phocoena sinus ), is estimated from four surveys conducted in Mexico between 1986 and 1993, using a variety of methods. A line‐transect approach was applied, using some parameters estimated from a related species, the harbor porpoise ( Phocoena phocoena...

ABSTRACf Sightings of 37 groups of vaquitas, Phocoena sinus, with an estimated total of 62 individuals, are reported from six major systematic surveys and four small boat surveys in the Gulf of California, Mexico, carried out between May 1992 and December 1993. All vaquita sightings but one occurred on the western side of the northern Gulf of Calif...

The consequences of accepting a false null hypothesis can be acute in conservation biology because endangered populations leave little margin for recovery from incorrect management decisions. The concept of statistical power provides a method of estimating the probability of accepting a false null hypothesis. We illustrate how to calculate and inte...

A microcomputer-based program named TRENDS implements the power analysis for detecting trends in abundance using linear regression described in Gerrodette, Ecology 68: 1364-1372 (1987) and Gerrodette, Ecology 72: 1889-1892 (1991). TRENDS is simple to use and allows easy calculation of statistical power, number of sampling occasions, sample precisio...