11 de enero de 2023

Using snout-to-vent measurement to determine if a newt is a juvenile or adult

The ImageJ software, developed by the National Institutes of Health (NIH), is a freeware tool for analyzing photographs. It is a useful tool for our purposes of measuring snout-to-vent length (SVL) of Pacific newts, especially those that are curved. As mentioned earlier, it is important to take special note of juveniles, since their loss has a disproportionate impact on population dynamics. For this project, we are defining juveniles as having a snout-to-vent length (SVL) of less than or equal to 5 centimeters or 2 inches.

For instructions, see the Newt Patrol Tutorial (2020-2021) below, section "Measuring Snout-to-Vent Length using ImageJ software":

https://drive.google.com/file/d/111Jdrnt_juRG6UP6TbQpVvRSOSrtd_6A/view

Publicado el 11 de enero de 2023 por truthseqr truthseqr | 0 comentarios | Deja un comentario

03 de diciembre de 2022

Exponential rise in juvenile newts killed this season (2022-2023)

This year @merav and team have recorded an astounding number of juvenile newts killed on the road, and the migration season is just beginning! This is an exponential increase over previous years. See Merav's blog post for more information:
https://www.bioblitz.club/post/an-unusual-beginning-of-the-newt-season

Juvenile newt roadkill doesn't remain on the road for long. Most of them will disappear within 24 hrs, so the reported numbers are an undercount of the total mortality. One study found that 80% of the smaller bodied amphibian carcasses were gone from the road within 24 hours. "... the combination of small, soft-bodied amphibians with warm, wet surfaces results in rapid carcass destruction, removal by scavengers or decomposition and thus leaves very little evidence of road mortality events.” (Santos et al., 2011; Zhang et al., 2018).

Juvenile newt deaths have a high impact on population viability. Some conservationists have found that amphibian population viability is not particularly sensitive to adult survival, therefore mitigations directed towards juveniles have a stronger effect on population viability than those that improve adult survival. Petrovan, et al. stated: "We conclude from the review of amphibian population models that there is substantial evidence that the fate of juveniles is critical and represents in many instances the driving factor for amphibian population dynamics...” (Petrovan, et. al., 2019, p 254)

JuvenilesPerSeason

Updated March 26, 2023.

Publicado el 03 de diciembre de 2022 por truthseqr truthseqr | 2 comentarios | Deja un comentario

24 de marzo de 2021

Tuesday, 3/23 - South half

Very windy day! Temps in upper 50s during survey, no rain. Saw the HTH truck.

55 dead newts, of which two were juveniles and most were dried ones.
13 vehicles
4 bicycles
1 Great Horned Owl feather (second time for the grove of eucalyptus, must be in there somewhere)

No luck teaching my goofy dog to be a newt-tracker.
;-)

Publicado el 24 de marzo de 2021 por anudibranchmom anudibranchmom | 0 comentarios | Deja un comentario

18 de enero de 2021

Juvenile Newt Mortality & Population Viability

The following information came from this fascinating paper:
Neglected juveniles; a call for integrating all amphibian life stages in assessments of mitigation success (and how to do it), (Silviu O. Petrovan and Benedikt R. Schmidt, Biological Conservation 236 (2019) 252–260))

  • Some juveniles apparently disperse diurnally in contrast to nocturnal dispersal in adults and their emigration has unpredictable timing and direction (they're not familiar with the landscape).
  • Juveniles cross the road in the opposite direction of adults. In other words, when the rainy season starts, juveniles emigrate away from vernal pools to the highlands while the adults are migrating from the highlands toward the vernal pools and reservoir.
  • Post-metamorphic juveniles are extremely small and are therefore more susceptible to dehydration on the road.
  • Juvenile carcasses don't stay on the road long. One study found that 80% of the smaller bodied amphibian carcasses were gone from the road within 24 h. "... the combination of small, soft-bodied amphibians with warm, wet surfaces results in rapid carcass destruction, removal by scavengers or decomposition and thus leaves very little evidence of road mortality events (Santos et al., 2011; Zhang et al., 2018)."
  • Some conservationists have found that amphibian population viability is not particularly sensitive to adult survival and mitigations directed towards post-metamorphic juveniles have stronger effects on population viability than those that improve adult survival.
  • The authors state: "We conclude from the review of amphibian population models that there is substantial evidence that the fate of juveniles is critical and represents in many instances the driving factor for amphibian population dynamics... p 254
  • The Gibbs & Shriver (2005) population model used by HTH takes into account juvenile survival rate. HTH used a hypothetical rate of 0.6 in their 2019 model. But it doesn't look like they're measuring the newts they're studying, so how will they differentiate juveniles from adults to come up with more than a hypothetical survival rate for juveniles?
Publicado el 18 de enero de 2021 por truthseqr truthseqr | 0 comentarios | Deja un comentario

17 de diciembre de 2020

Juvenile Newt Mortality at Lexington Reservoir (2019-2021)

Updated 2/19/21

The following graphs show the number of juveniles killed by vehicle collision on Alma Bridge Rd. at Lexington Reservoir between Jan. 2019 - Feb 2021.

Figure 1 shows that many more juveniles have been killed this year compared to previous migration seasons (~6% of total deaths). More than twice as many have been killed this year compared to last year. Also, more juveniles are killed in December than any other month, probably because juveniles begin to disperse from the lakes and streams in late fall with the first rains.

Figure 1.
Juveniles-0219

Figure 2 shows both juvenile and sub-adult newt mortality by newt size and migration season. Note that we didn't collect data on juveniles during the first season (2017-2018).

Figure 2.
Juv-Subadult-021921

Figure 3a shows the large increase in percentage of juvenile vs adults killed per season; Figure 3b shows that juvenile newt mortality is more severe in the northern half of our study area, which is recreational, compared to the southern half, which is residential.

Figure 3.
Juv-NS

Figure 4 shows juvenile newt mortality by newt size and migration season. These pie charts show the relative number of juveniles in each size category. (NR means the newt wasn't measured because no there was no reference scale in the picture or the newt was too smashed to accurately measure.)

Figure 4.
Juv-Subadult-02-0219

Publicado el 17 de diciembre de 2020 por truthseqr truthseqr | 10 comentarios | Deja un comentario

25 de julio de 2020

Dead Juveniles

I created this new subproject for the Pacific Newt roadkill study at Lexington Reservoir to track the dead juveniles, since they have a disproportionate impact on population size.

Volunteers, please enter the word "Juvenile" in the Notes or Tags field (or both) so that it's easy to search for and find these observations. As of this date, it's not possible to search for observations based on Annotations or Observation Fields.

How to Differentiate Juvenile from Adult Newts:

According to the Amphibiaweb accounts, the smallest recorded reproductive adult was 5 cm/2 in in snout to vent length (SVL), though there is variation and average adult size is 6.9-8.7 cm/2.7-3.4 in (SVL). So there is some fuzzy area, but this provides a conservative threshold.

If we estimate the tail length is about the same as the SVL, then total length of smallest reproductive adult recorded is about 10 cm/4 in.

• The terrestrial juvenile phase is called an eft.

References:
• "Neglected juveniles: a call for integrating all amphibian life stages in assessments of mitigation success (and how to do it)"
https://www.sciencedirect.com/science/article/abs/pii/S0006320718316306

• AmphibiaWeb: Taricha torosa
https://amphibiaweb.org/cgi/amphib_query?where-genus=Taricha&where-species=torosa&account=lannoo

https://amphibiaweb.org/cgi/amphib_query?where-genus=Taricha&where-species=torosa&account=amphibiaweb

Publicado el 25 de julio de 2020 por truthseqr truthseqr | 0 comentarios | Deja un comentario
Vida Silvestre es una entidad asociada a la Organización Mundial de Conservación