Ano Nuevo Research Articles

Water masses in the Monterey Bay during the summer of 2000

Water masses in Monterey Bay are determined from the CTD casts of the Monterey Ocean Observing System (MOOS) Upper-water-column Science Experiment (MUSE) August 2000 dataset. It is shown through cluster analysis that the MUSE 2000 CTD dataset contains 5 water masses. These five water masses are: bay surface water (BSW), bay warm water (BWW), bay intermediate water (BIW), sub arctic upper water (SUW) and North Pacific deep water (NPDW). The BWW is a new water mass that exists in one area and is attributed to the effects of solar heating. The volumes occupied by each of the water masses are obtained. The BIW water is the most dominant water mass and occupies 68.8% of the volume. The statistical means and standard deviations for each water parameter, including spiciness and oxygen concentration, are calculated during separate upwelling and relaxed periods. The water mass content and structure are analyzed and studied during upwelling and a relaxed period. During upwelling, along a CTD track off Pt. Ano Nuevo, the water mass T, S distribution tended to be organized along three branches. Off Pt. Ano Nuevo the innovative coastal observation network (ICON) model showed the formation of a cyclonic eddy during the analyzed upwelling period. In time the eddy moved southwest and became absorbed into the southerly flow during the initial phases of the following wind-relaxed period.

Delayed recovery of giant kelp near its southern range limit in the North Pacific following El Niño

The northern distribution limit of giant kelp, Macrocystis pyrifera (Agardh), along the Pacific coast of North America is relatively stable near Point Ano Nuevo, California, but its southern limit has varied over hundreds of kilometers along the Baja California peninsula during the past 20 years. The factors that drive this variability in the southern limit were examined by: (1) quantifying the abundances of M. pyrifera and the subsurface stipitate kelp, Eisenia arborea (Areschoug), near M. pyrifera’s then southern limit at Punta San Roque (27°15′N; 114°42′W) on ten occasions between August 1997 and June 2002 (prior to and following the 1997/1998 El Nino Southern Oscillation); (2) initiating a field manipulation at Punta San Roque in June 2000 to examine competition between these two kelp species; and (3) surveying 20 additional sites near Punta San Hipolito (27°01′N; 114°00′W) in June 2002 to determine whether M. pyrifera populations had recovered to their pre-1982/1983 El Nino southern range limit after ~20 years of absence. These observations and the experimental results suggest that M. pyrifera is removed from its southern limit by the high temperatures and large waves associated with El Ninos, while E. arborea is able to survive and recruit in high densities and thereby delay or even prevent M. pyrifera’s recovery. An inverse relationship was observed between these two species over the 5-year study. The field experiment showed that at both 4 months and 1 year after areas occupied by E. arborea were cleared, substantial recruitment of M. pyrifera occurred, while recruitment was negligible in uncleared areas. This study suggests that the southern range limit of M. pyrifera is determined by increased mortality and recruitment failure following the warm temperatures and low nutrient conditions associated with El Ninos, limited substrate availability, and by competition with the more persistent populations of E. arborea.

At-sea Activity and Diving Behavior of a Radio-tagged Marbled Murrelet in Central California

Abstract Radio-telemetry was used to continuously monitor the at-sea activity of an adult Marbled Murrelet (Brachyramphus marmoratus) nesting in Santa Cruz County, California. From 05.39 h on 28 May 1997, to 05.14 h on 29 May 1997, the murrelet was followed by tracking teams at Ano Nuevo Bay. Between 05.44 h and 20.19 h on 28 May, the bird engaged in eleven dive bouts, with a mean duration of 18.8 ± 5.4 min. Mean dive duration was 24.8 ± 15.7 s; mean surface between dives was 15.2 ± 12.7 s. No dives were initiated after 20.19 h. The bird spent 12.3% of the at-sea period and 23.4% of daylight hours engaged in diving bouts. This relatively small amount of time spent diving allows for considerable flexibility in activity budget.

MATERNAL TRAITS AND REPRODUCTIVE EFFORT IN NORTHERN ELEPHANT SEALS

The aim of this study was to determine the effects of maternal traits on reproductive expenditure and energy delivery to the offspring in a capital breeder, the northern elephant seal (Mirounga angustirostris). Changes in maternal and offspring energy reserves and milk-energy delivery were examined in relation to maternal parturition mass, body composition, and age in females and pups breeding at Ano Nuevo State Reserve, California. Maternal body mass and composition had significant effects on maternal energy expenditure over lactation. Path analysis suggested no significant effects of maternal age on reproductive effort of parous females. The efficiency of milk production increased significantly with maternal age. Offspring metabolism was a relatively small component of maternal energy expenditure, with pups storing 84% of the energy obtained from milk. These effects are an important consequence of the phocid strategy for enabling terrestrial parturition despite marine feeding. This strategy has resulted in an abbreviated and highly efficient lactation system that is strongly impacted by body reserves, linking foraging success at sea with reproductive success on land. Maternal size, body composition, and age were important features of reproduction in northern elephant seals. These characteristics are rarely considered concurrently in life history studies.

SPATIAL AND TEMPORAL VARIATION IN THE TIMING OF BIRTHS OF STELLER SEA LIONS

Abstract Throughout the range of the Steller sea lion (Eumetopias jubatus), nearly all births of full-term pups observed from 1968 to 1998 occurred between 15 May and 15 July. We found significant differences in timing of births between rookeries with the earliest mean date of birth (4 June) at Forrester Island, Alaska, and the latest (21 June) at Ano Nuevo Island, California. Mean date of birth becomes progressively later both north and south of Forrester Island. Births at individual rookeries were synchronous, with 90% of pups born within a 25-day period. We hypothesize that timing of births at rookeries is determined through selection for time periods when weather conditions are generally favorable for pup survival and when adequate prey items are predictably available near rookeries for lactating females. Temporal differences also were found in mean date of birth at 4 rookeries, with a maximum difference between earliest and latest mean date of birth of 10.2 days at Ano Nuevo Island. The most likely e...

The hunting strategy of white sharks ( Carcharodon carcharias ) near a seal colony

The degree to which white sharks, Carcharodon carcharias, are social while hunting is unclear. Our aim was to describe the behavior and interactions among white sharks hunting seals near a seal colony. We attached ultrasonic beacons to five adult white sharks, 4.5–5.2 m long, and recorded their movements and behavior toward each other over a 15-day period in October 1997 at Ano Nuevo Island, California. This site is home to colonies of four species of seals and sea lions. Two additional sharks, females 5.5 and 4.7 m in length, were later tracked intensively during periods of 12 and 3 days during October 1998 and November 1999, respectively. We recorded stomach temperature (indicative of feeding on warm-bodied seals) and swimming depths from the 5.5-m female, swimming speed and depth from the 4.7-m female. We monitored the movements and behavior of these sharks using an array of sonobuoys moored near the island; the receptive field measured 1 km2. Our principal findings were: (1) the sharks spent a mean time of 39.5% of each day patrolling within the receptive field; (2) no shark ever moved far out of it; (3) the sharks spent an equal amount of time and activity in the receptive field at all times of the day, daytime, twilight, and nighttime; (4) movements with respect to the island rookery were most often back and forth parallel to the shoreline, (5) tracks of three sharks, tagged at the same time and place, overlapped more often than those of the other two sharks; and (6) some sharks patrolled certain areas in the field preferentially, but there was no conclusive evidence that they defended these areas as territories. Feeding appeared to be infrequent: only two likely feeding bouts occurred during a cumulative 78-day/shark period that individuals were monitored at Ano Nuevo Island. The behavior and movements of the sharks were consistent with a hunting strategy, in which individuals search for prey independently but, at the same time, remain close enough to each other to “sense” and exploit a kill by any one of them by joining in on the kill to feed.

Radio-acoustic positioning as a tool for studying site-specific behavior of the white shark and other large marine species

We describe a method, radio-acoustic-positioning (RAP), for continuously monitoring the movements and behavior of large marine animals. An ultrasonic transmitter on the animal can be localized with high spatial accuracy (2 to 10 m) within an area of 1 km2, based on when the same pulse arrives at three hydrophones on sonobuoys aligned in a triangular array. Radio transceivers communicate with the base station, where the x and y coordinates of the subject are calculated using hyperbolic equations. The base station plots the individual's position and displays information from the tag's sensors in real time on a computer monitor before saving the data on a disk. The base station must be situated either on land or on a vessel within the reception range of the three buoys. We used a RAP system to monitor the movements and behavior of white sharks (Carcharodon carcharias) near the elephant seal rookery at Ano Nuevo Island in central California. This type of system is an ideal tool to study the predatory behavior of the white shark because individuals patrol for seal prey within a zone <1300 m from shore. We describe the operation of the system, including acoustic triangulation, range of detection and positioning, data acquisition and analysis, and positional accuracy. We illustrate the implementation of the method and its advantages and disadvantages by describing an ongoing study of white shark hunting-behavior. Sample data from this study are presented to illustrate specific points. We describe the movements of five sharks within the receiving range and their behavior relative to each other. The RAP system is compared to other complementary tracking methods. We conclude that this system has great potential for monitoring the movements and behavior of large marine animals within a relatively small zone, where feeding or reproduction takes place.

Abstract: Recurrence Intervals, Recency of Movement and Holocene Slip Rates Across the San Gregorio Fault Zone at Point Ano Nuevo, San Mateo County, California&amp;nbsp;

Abstract: Recurrence Intervals, Recency of Movement and Holocene Slip Rates Across the San Gregorio Fault Zone at Point Ano Nuevo, San Mateo County, California&amp;nbsp;

Age-Specific Natality of Northern Elephant Seals at the South Farallon Islands, California

We monitored 233 tagged, known-age female northern elephant seals ( Mirounga angustirostris ), age 3–16 years, that gave birth on the South Farallon Islands, 1975–1986. Females were from the 1970–1982 cohorts born on South Farallon, Ano Nuevo, San Nicolas, and San Miguel islands, California. Age-specific natality was significantly lower for 3- and 4-year olds (0.13 and 0.75, respectively), then stabilized at about 0.80 for females age 5–10 years. Natality was significantly lower in 1984 and 1985 than in other years. For the 1971–1980 cohorts, mean age at first reproduction ranged from 3.9 to 4.6 years. During this study, the age structure of females giving birth on the South Farallon Islands changed; mean age rose from 4 years in 1975 to 7 years in 1986. At least 20% of Farallon-born females survived to reproduce, ≥17% returned to the South Farallon Islands, and ≥ 3% emigrated to other rookeries. Females born at Ano Nuevo, San Miguel, and San Nicolas islands immigrated to the South Farallon Islands to give birth (≥3, ≥2, and >1% respectively). Mature, nonpregnant females were seen during the breeding season (6%), during the autumn haul out (15%), and during spring molt or a later breeding season (79%).

Life history consequences of variation in age at primiparity in northern elephant seals

The age when female northern elephant seals, Mirounga angustirostris, bear their first young varies from 2 to 6 years. At Ano Nuevo, California, a group of 77 females, primiparous at age 3, had a lower survivorship rate to each successive year up to age 8 than a group of 98 females that deferred initial pupping until age 4. The difference in survivorship appears to be due to the greater relative energetic costs of gestation and lactation incurred by the earlier breeding females during a period in their development when growth is rapid. An alternate hypothesis for the difference in survivorship — that young primiparous females are in poor condition from birth-is untenable; females that pupped early in life were larger at weaning age (a correlate of condition) than females that were primiparous 1 year later.

Sexual Behavior of Male Northern Elephant Seals: I. Lethal Injuries To Adult Females

[Adult female mortality of northern elephant seals, Mirounga angustirostris, was monitored daily throughout the breeding season and weekly during the non-breeding season at Ano Nuevo, California, during the period 1968 to 1987. Behavioral observation and necropsy findings were collected and circumstantial evidence was compiled to determine the cause of death. Female deaths on the rookery were rare; only 17 female deaths were recorded over the 20 year period. Cause of death could not be estimated in three cases because of advanced decomposition, one female died from an accident, and two others had no apparent trauma. The majority of deaths (11) were caused by traumatic injuries inflicted by males during mating attempts as the females departed harems for the sea at the end of lactation. Mortalities caused by males were distributed across a broad age range. Based on the observed incidence of female mortality in relation to females present on the rookery, the probability of a female being killed by a male during the breeding season is about one in a thousand. Females are expected to evolve adaptations to reduce injurious encounters with males. Females are injured and killed by males during mating attempts in a variety of species. A hypothesis concerning the conditions under which female animals sustain potentially lethal injuries during mating is advanced., Adult female mortality of northern elephant seals, Mirounga angustirostris, was monitored daily throughout the breeding season and weekly during the non-breeding season at Ano Nuevo, California, during the period 1968 to 1987. Behavioral observation and necropsy findings were collected and circumstantial evidence was compiled to determine the cause of death. Female deaths on the rookery were rare; only 17 female deaths were recorded over the 20 year period. Cause of death could not be estimated in three cases because of advanced decomposition, one female died from an accident, and two others had no apparent trauma. The majority of deaths (11) were caused by traumatic injuries inflicted by males during mating attempts as the females departed harems for the sea at the end of lactation. Mortalities caused by males were distributed across a broad age range. Based on the observed incidence of female mortality in relation to females present on the rookery, the probability of a female being killed by a male during the breeding season is about one in a thousand. Females are expected to evolve adaptations to reduce injurious encounters with males. Females are injured and killed by males during mating attempts in a variety of species. A hypothesis concerning the conditions under which female animals sustain potentially lethal injuries during mating is advanced.]

Magnetostratigraphy: An Excellent Tool for Much-Needed Numerical Age-Dating in the Monterey Formation of California

Numerical age-dating and long-range intra- and interbasin correlation have been hampered in the petroleum-bearing Miocene Monterey Formation of California. This stems mainly from the poor preservation of age-diagnostic siliceous microfossils, the majority of which were totally destroyed by wholesale diagenesis during burial. Paleomagnetism offers a powerful stratigraphic tool of great promise for absolute age-dating in the Monterey and, for this reason, the authors are conducting a detailed study of the Monterey in five widely separated basins in coastal California. The results of their study of the Monterey at Shell Beach (Pismo basin) and Point Ano Nuevo (outer Santa Cruz basin), which is the only study that provides precise numerical ages for the Monterey rocks, clearly confirm the potential that paleomagnetism and magnetostratigraphy hold toward improving their basic understanding of the Monterey Formation.

Frontier Tertiary Basins with Promising Hydrocarbon Potential, Offshore California

Dwindling domestic petroleum reserves have drawn attention to areas of promising potential within the United States. The federal outer continental shelf (OCS) off of California remains one of the most likely sources of future domestic oil and gas. The Federal Government, as mandated by the OCS Lands Act, must evaluate the OCS for hydrocarbon potential and to make promising areas available for exploration and production. Offshore Eel River basin, for example, contains the extension of the gas-producing Table Bluff trend. Seismic sections display amplitude and velocity anomalies, suggesting the possible presence of gas in offshore structures. Faulting, folding, and a thick Neogene marine section indicate a high probability of traps and source rocks being present. A moderately thick Neogene section and excellent structural development is observed in the southern Point Arena basin. The few wells previously drilled indicate mature source rocks are locally present and fractured reservoir potential is good to excellent. The structural geology of northern Bodega basin resembles that of Point Arena basin. Stratigraphic analogies are also evident, and the Neogene section appears to be thicker. This area should be considered a favorable petroleum habitat. Ano Nuevo basin displays many similarities to the Santa Maria and Salinas basins.more » The structural development provides trapping mechanisms, and the two offshore wells indicate mature source rocks. The reservoir potential is fair to excellent. Capistrano basin may be the least known of all the frontier offshore basins. Structural similarities to the Los Angeles basin suggest the likely formation of trapping mechanisms. Should stratigraphic similarities exist, then its oil and gas potential would be considered quite favorable.« less

Sexual Behavior of Male Northern Elephant Seals: Ii. Female Response To Potentially Injurious Encounters

[During mating attempts by males, female elaphant seals, Mirounga angustirostris, are sometimes injured or killed as they return to sea at the end of lactation. We tested two predictions from the general hypothesis that females behave in a way that reduces the possibility of injury or death from sexual encounters with males: 1) departing females attempt to avoid males, and 2) if males cannot be avoided, departing females exhibit sexually receptive behavior to males, and thereby reduce the threat of injury from aggressive mating attempts. Circumstances surrounding the departure of 336 females from harems on the Ano Nuevo rookery in central California were recorded over the course of nine breeding seasons from 1982-1990. Females did little to avoid encounters with males surrounding harems; they did not leave in greater numbers at night, in groups, or during disturbances on the harem periphery. They did, however, leave harems preferentially at high tide which reduced the distance to the water and shortened transist time. Most departing females did not resist the mating attempts of peripheral males but, rather, they were unusually receptive. Receptive females received fewer blows capable of producing injury than resisting females. We conclude that receptive behavior in this context buys safe passage. It is an effective means of reducing male aggression and the probability of injury; a male has no need to restrain a receptive female with blows, and should the most dominant male in the area copulate with a departing female, he frequently escorts her to sea and defends her from other males., During mating attempts by males, female elaphant seals, Mirounga angustirostris, are sometimes injured or killed as they return to sea at the end of lactation. We tested two predictions from the general hypothesis that females behave in a way that reduces the possibility of injury or death from sexual encounters with males: 1) departing females attempt to avoid males, and 2) if males cannot be avoided, departing females exhibit sexually receptive behavior to males, and thereby reduce the threat of injury from aggressive mating attempts. Circumstances surrounding the departure of 336 females from harems on the Ano Nuevo rookery in central California were recorded over the course of nine breeding seasons from 1982-1990. Females did little to avoid encounters with males surrounding harems; they did not leave in greater numbers at night, in groups, or during disturbances on the harem periphery. They did, however, leave harems preferentially at high tide which reduced the distance to the water and shortened transist time. Most departing females did not resist the mating attempts of peripheral males but, rather, they were unusually receptive. Receptive females received fewer blows capable of producing injury than resisting females. We conclude that receptive behavior in this context buys safe passage. It is an effective means of reducing male aggression and the probability of injury; a male has no need to restrain a receptive female with blows, and should the most dominant male in the area copulate with a departing female, he frequently escorts her to sea and defends her from other males.]

Parental investment and the secondary sex ratio in northern elephant seals

Data on northern elephant seals, Mirounga angustirostris, bearing on sex ratio theory were collected at Ano Nuevo, California, and other Californian and Mexican Islands, during the period 1967 to 1988. The mass of males exceeded that of females by 7–8% at birth and at weaning. The sex ratio was biased to males at birth (51.2%) and was near unity at weaning (49.6% males). The sex ratio did not vary as a function of maternal age or maternal mass except in 6-year-old females, who produced significantly more males. Although sons cost more to rear in energetic terms than daughters, and mothers were more successful weaning the latter, the sex of the pup reared exerted no significant effect on the mother's reproductive performance the following year or on her subsequent survival. These data suggest that parents invest equally in sons and daughters when investment is measured in terms of future reproduction (Fisher 1930) and provide no support for the theory of adaptive shifts in sex ratio (Trivers and Willard 1973). The small sex difference in mass due to maternal effort reflects the fact that females fast during lactation and all energy transferred is from limited body stores. Because of these circumstances, selection for superior condition at the end of the period of parental investment may act more strongly on pups, who have the opportunity to steal milk, than on their mothers.

DYNAMIC RESPONSE ANALYSIS. III. A CONSISTENCY FILTER AND APPLICATION TO FOUR NORTHERN ELEPHANT SEAL COLONIES

AbstractDynamic response analysis, a technique for determining stock size relative to the maximum net productivity level (MNPL), was applied to northern elephant seal populations from the South Farallon Islands, Año Nuevo Island, San Nicolas Island and San Miguel Island. Pup counts were used as indices of population size. The application of dynamic response analysis presented here involved some methodological innovations. We present a moving interval method which involves calculating separate dynamic response analyses for intervals of various lengths ranging from four counts to the total number available for the colony. The sign of the second order polynomial regression coefficient computed from a particular interval was used to indicate the colony's apparent status (relative to its MNPL, += above MNPL, ‐ = below MNPL) on that interval. Consistency in the sign of the second order coefficient, as the interval was moved along the trajectory, was used to determine the minimum reliable interval size. Each colony exhibited growth similar to that of a population below its MNPL. These results are consistent with recent natural history observations at San Nicolas, San Miguel and the South Farallon islands. Natural history observations at Año Nuevo Island suggest that the colony there is now at equilibrium. Thus, if our results from dynamic response analysis of the Ano Nuevo colony are correct, it appears that the MNPL may be close to the carrying capacity for these animals.

Diatom Biostratigraphy of Chert Intervals in Santa Maria and Other Neogene Basins, California: ABSTRACT

Chert is a common component of the Monterey Formation in many outer Neogene basins. Successful recovery of diatoms from dolomite beds and concretions, which are sufficiently abundant in chert-bearing sections, makes diatom biostratigraphic analyses possible in several poorly chronicled Neogene basins. At Ano Nuevo in the Outer Santa Cruz basin, where the section consists mainly of porcelanite and chert, diatom biostratigraphy yields an age duration from 14.7-13.4 Ma. Precise age control allows analysis of cyclical aspects of chert and dolomite to be carried out on the section. Frequency estimates of silica-carbonate cycles at Ano Nuevo suggest that the cycles may be related to early middle Miocene paleo-oceanographic events. In the Santa Maria basin, where black quartz cherts are widespread, diatom biostratigraphy has been successfully applied on the Mussel Rock, Lions Head, and Shell Beach sections. Preliminary data suggest black chert intervals are strongly age controlled and are possibly related to Miocene cooling events that affected the Santa Maria basin. Ongoing studies of the diatom biostratigraphy of dolomites promise improved age control in the Santa Maria basin. This will not only aid in paleo-oceanographic interpretations, but will also improve constraints on tectonic and depositional aspects of the basin.

Age and Paleo-oceanographic Significance of Silica-Carbonate Cycles in Miocene Monterey Formation, California: ABSTRACT

Middle Miocene Monterey Formation cherts are often cyclically interbedded with laminated dolomites. Their co-occurrence is paradoxical because cherts are produced in relatively cold water, whereas dolomite is associated with warm water. Chert and dolomite intervals generally have poor age control, which has hindered further paleo-oceanographic interpretations. Examination of diatom assemblages that are well preserved in the dolomites has resulted in high-resolution age dating and estimation of cycle duration in 200 m of section exposed at Pt. Ano Nuevo, northern California. The age of the section ranges from late Luisian to early Mohnian, at approximately 15-12 Ma. Cycle duration estimates for the Pt. Ano Nuevo section imply that the chert-dolomite cycles may be on the order of 100,000 and 50,000 years. Such durations are consistent with, and were perhaps influenced by, changes in the earth's orbital parameters (Milankovich cycles), namely eccentricity and tilt. Warm and cold cycles have been identified by previous investigators in nondiagenetically altered middle Miocene sections of the Monterey Formation and in northeastern Pacific DSDP cores. These cycles are recognized and dated by the use of abundance fluctuations of planktonic foraminifera and diatoms. The chert-dolomite cycles are likely time equivalent to the microfossil-based cold-warm cycles and further strengthenmore » the paleo-oceanographic and paleoclimatic interpretation.« less

California Sea Lions Breeding at Ano Nuevo Island, California

L'extension vers le nord des sites de reproduction de Zalophus californicus pourrait resulter d'un accroissement continu de population de Californie et du Mexique toute entiere au cours de ce siecle

The Patagonian Batholith S of Tierra del Fuego, Chile: timing and tectonic implications

Reconnaissance field studies on the Patagonian Batholith exposed S of Tierra del Fuego, together with 49 new K-Ar and Rb-Sr mineral dates, render new insights into two main aspects of the late Mesozoic geology: the geochronology and composition of the batholith, and time relations between the emplacement of the plutons and deformation. The envelope of the batholith in this area is mainly composed of late Jurassic-early Cretaceous sedimentary and volcanic rocks formed in an island arc-marginal basin system. Three main plutonic groups have been recognized which have yielded mineral dates, interpreted as crystallization ages, ranging from 141 to 34 Ma. The earliest is a gabbroic assemblage, including gabbros, diorites and hornblendites exposed as relicts within later granitoids and with dates ranging from 141 to 103 Ma. The Canal Beagle Plutonic Group is composed of granitoids characterized by a penetrative syn-magmatic foliation and with dates of 113 to 81 Ma. The Seno Ano Nuevo Plutonic Group is formed of granitoids with dates of 60 to 34 Ma and is mainly exposed in the outer islands, indicating a local oceanwards shift of plutonism with time. Lower Cretaceous island arc volcanism was contemporaneous with the intrusion of the gabbroic assemblage, and, in part at least, of the Canal Beagle Plutonic Group. Folding of the marginal basin infill, which has been related to the closure of the marginal basin, occurred from about 100 to 93 Ma ago. The gabbroic assemblage was apparently mainly pre-tectonic, whereas the Seno Ano Nuevo Plutonic Group was clearly intruded after this deformational event. A post-tectonic or possibly late-tectonic emplacement for the youngest plutons of the Canal Beagle Plutonic Group and a pre- or syn-tectonic intrusion for the oldest is inferred.